Germanium

Typical wastewaters

• optical fibre industry wastewater low concentration germanium in fibre optics industry wastewater, complexed by desferrioxamine B at low pH over 80 percent recovered at 84.5 percent purity from real fibre optics wastewater
• lead smelter slag washing wastewater germanium with Zn and Fe(II) in acidic slag washing water; precipitated selectively with tannic acid at pH 3 to 6 96.6 percent Ge precipitation in 2 minutes; treated water reused
• solar panel manufacturing wastewater germanium ion together with silicate ion; adsorbed as a catechol anion complex on a quaternary ammonium membrane at pH 3

1 · Identity

Symbol, number

Ge, 32

Oxidation states in water

+4 as germanic acid Ge(OH)₄ and its anion, plus the methylated Ge(IV) species monomethylgermanium and dimethylgermanium

Note

The element entry covers the metalloid and GeO₂. In water germanium follows silicon: germanic acid is taken up with silicic acid and cycles with biogenic silica in the ocean (the review's statement; the Ge/Si ratio literature was not read).

2 · Occurrence in water

Natural sources

Weathering of silicate rock releases germanic acid with silicic acid; siliceous organisms take it up and it cycles with silica in the ocean. Methylgermanium species are a separate, unreactive dissolved pool.

Anthropogenic sources

Fibre optic, infrared optic, semiconductor and solar manufacture (element entry); coal combustion residues (germanium rich lignites in the element entry). No effluent concentration was read.

3 · Speciation

Inorganic germanium is the neutral tetrahydroxide Ge(OH)₄ (germanic acid) in neutral water, deprotonating to the anion in alkaline water; the methylated species CH₃Ge(OH)₃ and (CH₃)₂Ge(OH)₂ are stable, unreactive and dominate the total in seawater. Ge(IV) is not reduced in natural water.

Solubility

GeO₂ dissolves to germanic acid; no solubility figure was read.

Hydrolysis

Germanic acid is a weak acid like silicic acid; the first deprotonation matters only in alkaline water (no pKa read this session).

Complexation

No complexation data read; the methyl species are covalent, not complexes.

Precipitates

None in natural water; germanium leaves solution inside biogenic opal and with iron oxides.

4 · Role in treatment

Not relevant or not given for this element.

5 · Removal and control

Not relevant or not given for this element.

6 · Analytics

Sampling pitfalls

Blank control decides the result at ng/L: the speciation method reports a procedure to minimise inorganic Ge blanks from reagents and water. Methylgermanium does not demethylate during hydride generation in the Tris-cysteine medium, so speciation survives the analysis.

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

No drinking water guideline. Germanium is not an essential element and its acute toxicity is low, but at least 31 human cases linked prolonged intake of germanium supplements (dioxide, carboxyethyl germanium sesquioxide, lactate citrate; total doses 15 to over 300 g over 2 to 36 months) with renal failure and death, with kidney tubular degeneration, anaemia, muscle weakness and peripheral neuropathy; recovery of renal function was slow and incomplete. A lifetime drinking water study in animals at 5 ppm germanium gave tissue accumulation and impaired kidney and liver function.

Bioaccumulation

Fish and seafood 1 to 5 ng/g (mean 2 ng/g); mussel reference material 68 ng/g (review).

Ecotoxicity

No aquatic ecotoxicity value was read.

Flags

• The 5 ppm drinking water animal study is quoted from the 1997 hazard assessment abstract; species and duration beyond lifetime are not given there.
• Fresh water concentrations (0.011 to 0.022 µg/L for tap, river and seawater) appeared only in a search summary and are not written.
• The silicon analogy (uptake into biogenic opal, river and ocean Ge/Si ratios) rests on the Frontiers review and on search summaries of the 1985 and 1988 germanium papers, which were not reachable; no ratio is written.

Gaps

• No river, groundwater, geothermal, municipal or industrial wastewater concentration was read (the 1988 review of germanium biogeochemistry and the geothermal papers were not reachable).
• No pKa of germanic acid or solubility of GeO₂ was read.
• No removal process for germanium from water was read; none is practised.
• No GCC discharge standard was read.
• No aquatic ecotoxicity data were read.

Sources

Identity

Name and symbol

Germanium, Ge

Atomic number

32 protons

Position

group 14 · period 4 · p-block · metalloid

CAS number

7440-56-4

Atomic structure

Atomic mass

72.63 u

Electron configuration

1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p²
[Ar] 4s²³d¹⁰⁴p²

Electrons per shell

2, 8, 18, 4

Valence electrons

4 outer shell

Physical properties

State at room temperature

Solid

Melting point

1,211.4 K (938.25 °C)

Boiling point

3,106 K (2,832.85 °C)

Density

5.323 g/cm3

Appearance

grayish-white

Thermal conductivity

60.2 W/(m·K)

Electrical resistivity

1 Ω·m at 20 °C

Electrical conductivity

1 S/m

Crystal structure

diamond cubic

Molar heat capacity

23.222 J/(mol·K)

Chemical properties

Oxidation states

+4, +2

Electronegativity

2.01 (Pauling Scale)

Ionisation energy

7.9 eV
1st 762, 2nd 1,537.5, 3rd 3,302.1 kJ/mol

Electron affinity

1.35 eV

Atomic radius

empirical 120, covalent 120, van der Waals 211 pm

Ionic radius

Ge²⁺ 73; Ge⁴⁺ 53 pm

Reactivity

A metalloid of group 14 between silicon and tin, fairly inert at room temperature: it keeps its lustre in air, resists dilute acids and alkalis, and shows +4 chemistry with some +2 compounds.

with water

Does not react with water.

with oxygen, air

Stable in air at room temperature; begins to oxidise slowly at about 250 C to germanium dioxide: $\ce{Ge + O2 -> GeO2}$.

with acids

Insoluble in dilute acids and alkalis; dissolves slowly in hot concentrated sulfuric and nitric acid, and reacts violently with molten alkalis to give germanates.

with halogens

Burns in chlorine to the volatile tetrachloride, a fuming liquid: $\ce{Ge + 2 Cl2 -> GeCl4}$; the four tetrahalides GeF4, GeCl4, GeBr4 and GeI4 are all known.

Typical compounds

• GeO₂ germanium dioxide white powder; infrared optics, PET polymerisation catalyst
• GeCl₄ germanium tetrachloride fuming liquid distilled to purify germanium
• GeH₄ germane methane-like hydride, semiconductor gas
• GeS₂ germanium disulfide binary chalcogenide
• Ge(C₂H₅)₄ tetraethylgermane typical organogermanium compound from GeCl4

Occurrence, production and use

Crustal abundance

1.5 milligrams per kilogram

Oceanic abundance

5×10-5 milligrams per liter

Occurrence and sources

The metal is found in

▸ argyrodite, a sulfide of germanium and silver;

▸ germanite, which contains 8 percent of the element;

▸ zinc ores;

▸ coal; and

▸ other minerals

The element is commercially obtained from the dust from smelters that process zinc ores. It is also recovered from combustion by-products of certain coals.

Germanium can be separated from other metals by fractional distillation of its volatile tetrachloride. These techniques permit the production of germanium of ultra-high purity.

• argyrodite (Ag8GeS6) and germanite rare minerals; the Freiberg silver mines of the 1886 discovery; germanite holds about 8 percent germanium
• trace germanium in zinc and lead zinc copper sulphide ores zinc concentrates from Alaska and Tennessee, zinc smelter residues in China (Yunnan) and Canada, tailings in Congo (Kinshasa); reserves not reported at mine or country level
• germanium in lignite coal recovered from combustion by products of certain coals

Extraction, production

Recovery from zinc smelter residues and refining through the tetrachloride

Germanium bearing zinc concentrate goes to smelters that recover it as an intermediate leach concentrate or as dioxide and tetrachloride; the tetrachloride is purified by fractional distillation and converted to dioxide and to zone refined metal with impurities below one part in ten billion. The sources name the steps but state no reaction, so no equation is written. United States imports of metal and dioxide were about 33,000 kilograms of germanium content in 2024 (estimate).

Uses

The largest use of germanium is in the semiconductor industry. When doped with small amounts of arsenic, gallium, indium, antimony or phosphorus, germanium is used to make transistors for use in electronic devices. Germanium is also used to create alloys and as a phosphor in fluorescent lamps. Both germanium and germanium oxide (GeO) are transparent to infrared radiation and are used in infrared optical instruments and infrared detectors. Some germanium compounds seem to be effective in killing some types of bacteria and are currently being studied for use in chemotherapy.

When germanium is doped with arsenic, gallium, or other elements, it is used as a transistor element in thousands of electronic applications. The most common use of germanium is as a semiconductor. Germanium is also finding many other applications including use as an alloying agent, as a phosphor in fluorescent lamps, and as a catalyst.

Germanium and germanium oxide are transparent to the infrared and are used in infrared spectroscopes and other optical equipment, including extremely sensitive infrared detectors.

The high index of refraction and dispersion properties of its oxide's have made germanium useful as a component of wide-angle camera lenses and microscope objectives.

The field of organo-germanium chemistry is becoming increasingly important. Certain germanium compounds have a low mammalian toxicity, but a marked activity against certain bacteria, which makes them useful as chemotherapeutic agents.

• Fibre optics and infrared optics: germanium dioxide and tetrachloride as dopants in optical fibre glass for data networks and telecommunications; germanium metal lenses and windows for infrared optical systems, routinely recycled from machining scrap and decommissioned equipment fibre optics was the largest United States end use in 2024, then infrared optics, semiconductors and solar cells, and radiation detectors (USGS, ranking only)
• Electronics and space solar: germanium wafers as substrates for multijunction solar cells on satellites; germane gas for semiconductor and solar cell manufacture; high purity germanium radiation detectors; doped germanium transistors, now largely replaced by other semiconductors
• Chemicals: germanium dioxide as a polymerisation catalyst for polyester, a use implied by USGS naming antimony and titanium as its substitutes in that role; a thin link, flagged in the gaps
• Mining: germanium leaves the ground in zinc concentrate, so its extraction footprint is that of the base metal sector of the MWEI BREF

Safety, toxicity

GHS classification, signal word Danger

• H228 Flammable solid Flammable solids
• H361 Suspected of damaging fertility or the unborn child Reproductive toxicity
• H373 May causes damage to organs through prolonged or repeated exposure Specific target organ toxicity, repeated exposure
• H412 Harmful to aquatic life with long lasting effects to the aquatic environment, long-term hazard

Discovery and name

Discovered by

Clemens Winkler

Discovered

1886

First isolated

not in sources

Named by

not in sources

Origin of the name

after Germany, homeland of the discoverer

The element is a gray-white metalloid. In pure state, the element is crystalline and brittle, retaining its luster in air at room temperature. It is a very important semiconductor. Zone-refining techniques have led to production of crystalline germanium for semiconductor use with an impurity of only one part in 1010.