Gallium - Ga

Gallium (Ga) is a low-melting metal important to electronics and specialised alloys. This guide outlines its properties, uses, exposure considerations and the assessment of gallium-bearing water streams.

Chemical properties · Uses and occurrence · Health effects · Environmental effects · Water and treatment

Chemical properties of gallium

Selected properties of gallium
Symbol / atomic number	Ga / 31
Group / period / block	13 / 4 / p
Standard atomic weight	69.723(1)
Electron configuration	[Ar] 3d¹⁰ 4s² 4p¹
Common oxidation state	+3
Density (solid, near room temperature)	5.91 g cm⁻³
Melting point	29.7646 °C
Boiling point	2229 °C
Electronegativity (Pauling)	1.81
Non-bonded atomic radius	0.187 nm
Covalent radius	0.123 nm
First ionisation energy	578.8 kJ mol⁻¹
Naturally occurring isotopes	⁶⁹Ga and ⁷¹Ga
Discovery	Paul-Émile Lecoq de Boisbaudran, 1875
CAS registry number	7440-55-3

Atomic weight follows CIAAW; parentheses indicate uncertainty in the final digits. Physical properties follow the Royal Society of Chemistry. Atomic radii depend on their definition.

Silvery gallium sample in a shallow holder — Gallium sample.

Uses, occurrence and history

Gallium is a soft, silvery metal that melts just above ordinary room temperature. Its low melting point makes it useful in low-melting alloys. Gallium metal should be distinguished from compound semiconductors such as gallium arsenide (GaAs) and gallium nitride (GaN), which have different properties.

Gallium-based semiconductors are used in integrated circuits, light-emitting diodes, laser diodes, photodetectors and solar cells. The properties of the compound, rather than those of pure gallium metal, enable these applications.

Gallium occurs in small concentrations in several minerals and is recovered as a by-product of processing bauxite and zinc-bearing materials. Its dispersed occurrence makes recovery dependent on the host material and processing route. Production and supply data are available from the US Geological Survey.

Paul-Émile Lecoq de Boisbaudran discovered gallium in 1875. Its properties helped confirm Mendeleev's prediction of a missing element below aluminium in the periodic table.

Health effects of gallium

Gallium has no established essential biological role in humans. The metal, soluble salts, semiconductor compounds and radioactive gallium preparations should not be treated as having the same health effects. Risk depends on the chemical form, dose and route of exposure.

Gallium arsenide presents an important occupational hazard. Inhaled or ingested particles can release biologically available inorganic arsenic; NIOSH recommends controlling exposure to these particles. Cutting, grinding or polishing semiconductor material can create dust requiring appropriate engineering controls and handling procedures.

Gallium-67 citrate is used in diagnostic nuclear medicine under professional supervision. This does not mean that radioactive gallium is harmless: its prescribing information describes radiation precautions and possible adverse reactions, including allergic reactions, rash and nausea. Medical use is distinct from environmental or workplace exposure.

Environmental effects of gallium

Gallium occurs naturally in mineral deposits. Mining, refining and semiconductor processing can create gallium-containing residues and waste streams. An environmental assessment should identify the compounds present, their concentrations and associated contaminants. A stream containing gallium arsenide also requires assessment of arsenic.

The presence of gallium alone does not demonstrate either environmental safety or ecological damage. Site-specific exposure data and the composition of the material are needed to assess risk and select appropriate waste management.

Gallium in water and treatment

For a gallium-bearing process stream, establish the gallium concentration, pH, dissolved and suspended fractions, and other constituents before selecting treatment. Treating contaminated rinse water and recovering gallium from a concentrated process liquor are different objectives.

Laboratory research has demonstrated pH-dependent hydrolysis and precipitation of Ga(III) in sulfate solutions. Controlled precipitation with subsequent solids separation is therefore a treatment route to investigate, rather than a guaranteed removal process. The actual water composition, temperature and operating conditions must be assessed through treatability tests.

Where arsenic-containing materials are processed, measure arsenic separately and consider its treatment requirements alongside gallium. Further information: arsenic in water and heavy-metal removal.

Gallium page last reviewed: 24 October 2026 by Lenntech.