Europium

Typical wastewaters

• coal mine drainage (acid) Eu³⁺ and the EuSO₄⁺ ion pair dissolved at low pH in sulfate rich drainage; total rare earths averaged 282 µg/L over 141 Appalachian sites, per-element values not read co-precipitates into the iron, aluminium and manganese hydroxide sludge when the drainage is neutralised
• nuclear site discharges (UK monitoring) fission products Eu-154 and Eu-155 (half-lives 8.80 and 4.96 years) as Eu³⁺, listed in the RIFE radionuclide data tables monitoring tables only; discharge quantities were not read

1 · Identity

Symbol, number

Eu, 63

Oxidation states in water

+3 only (Eu³⁺)

Note

The metal's reactions are in the book entry; in water europium shares the trivalent carbonate and phosphate chemistry of the lanthanide row.

2 · Occurrence in water

Natural sources

Weathering of monazite and bastnaesite; the middle lanthanide most depleted from feldspar bearing rocks (negative Eu anomaly of shale) and enriched in hydrothermal fluids where Eu(III) is reduced to the larger, more soluble Eu(II). In seawater Eu/Eu* is 0.88 to 1.15; negative Eu anomalies appeared in an organic carbon reactive barrier at low Eh with methane and sulfide present, suggesting reduction even at low temperature.

Anthropogenic sources

No europium point source to water was read. Fission products Eu-154 and Eu-155 appear in the RIFE radionuclide data tables for UK nuclear site monitoring (half-lives 8.80 and 4.96 years); discharge quantities were not read.

3 · Speciation

Trivalent Eu³⁺ throughout the natural pH and Eh range. Below about pH 6, and in sulfate rich water such as mine drainage, the free ion and the EuSO₄⁺ ion pair dominate (sulfate complexes above 90 percent at pH 3.1 to 3.4 in the EPA groundwater study). From neutral to alkaline pH the carbonate complexes EuCO₃⁺ and Eu(CO₃)₂⁻ take over, and they bind the heavy lanthanides more strongly than the light ones (at pH 5.1 to 6.1 the carbonate share rose from 5.0 percent for La to 19.2 percent for Lu). Phosphate, carbonate and fluoride solids and sorption to iron and manganese oxides cap the dissolved concentration at ng/L in oxic neutral water, and the light lanthanides ride partly on colloids. Europium adds a reduction step under strongly reducing conditions: Eu³⁺ to Eu²⁺, which no longer follows the trivalent lanthanides.

Solubility

Controlled by the phosphate, carbonate and fluoride solids and by sorption; the RIVM report puts total dissolved lanthanum and cerium in Dutch surface water at about 1 µg/L or less and the free ion fraction at 0.3 fM to 9 pM. No solubility product for a europium solid was read this session.

Hydrolysis

Hydrolysis of Eu³⁺ is minor in natural water; the hydroxide Eu(OH)₃ forms only at high pH, so lime or caustic neutralisation of acid mine water strips the element with the iron and aluminium hydroxides rather than as its own hydroxide (no hydrolysis constant read this session).

Complexation

Sulfate at low pH, carbonate at neutral to alkaline pH (the sources read); humic substances compete for the element in organic rich water and are out-competed by carbonate in alkaline water. No stability constants were read this session.

Precipitates

EuPO₄ (hydrated), Eu₂(CO₃)₃, Eu(OH)₃ under lime; Eu(III) compounds are far less soluble than the corresponding Ce(III) compounds (Dahle and Arai).

4 · Role in treatment

Not relevant or not given for this element.

5 · Removal and control

6 · Analytics

Sampling pitfalls

Filtration defines the result: 0.2 or 0.45 µm filtrates still carry colloid bound lanthanides, and only ultrafiltration (10 kDa) separates the truly dissolved pool, which matters most for the light lanthanides. Acidify after filtration. Report the shale-normalised pattern so that anthropogenic anomalies (gadolinium, lanthanum, samarium) are visible. The ISO 17294-2 element list as read this session does not name europium, so the method's applicability must be checked against the standard itself. Eu is a natural neighbour for interpolating Gd* and was used in the Rhine work to quantify anthropogenic Sm, although its own redox anomalies can decouple it from the row.

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 human health guideline; no toxicity data for europium were read this session.

Bioaccumulation

Field bioconcentration factors in Rhine estuary amphipods fall from the light to the heavy lanthanides (La 28,840 to Lu 4,786; Eu 11,220); carp muscle takes up little (BCF 0.22 to 1.10 for Ce, La, Nd, Pr, Sm) while internal organs reach 634 to 978. Anthropogenic La and Sm in the Rhine are taken into mussel shells, anthropogenic Gd is not, so speciation decides bioavailability.

Ecotoxicity

No MPC was derived for europium: the RIVM report set risk limits only for Y, La, Ce, Pr, Nd, Sm, Gd and Dy. The one europium number it carries is a field bioconcentration factor in amphipods of 11,220 (porewater basis).

Flags

• The RIVM MPCs, where they exist, are environmental risk limits from a 2000 report (LC₅₀ divided by 1000, background at the detection limit), not permit limits.
• The seawater range is one western Pacific station.
• The Eu reduction half reaction is written here; the sources describe the anomaly and infer reduction but print no equation.
• Europium's absence from the ISO 17294-2 list may be an omission in the catalogue summary read.

Gaps

• WHO GDWQ and EU DWD 2020/2184 Annex I were not read this session (eur-lex returned the articles without the annexes), so their absence of a rare earth parameter is not asserted here; only the US EPA table was read.
• No GCC discharge standard was read; no GCC row is written.
• World average river water concentrations (Gaillardet et al. 2003) were not reachable; river figures come from the Rhine and Dutch waters only.
• No source read this session gives municipal wastewater concentrations for this element beyond the gadolinium literature.
• ICP-MS oxide interference corrections between lanthanides are standard practice but no method text describing them was read, so none is written.
• No stability constants or solubility products for this element's carbonate, phosphate or hydroxide were read; the speciation is qualitative, taken from the EPA groundwater study and the RIVM report.
• No europium concentration in rivers or groundwater was read.
• No Eu-154 or Eu-155 discharge quantity was read.

Sources

Identity

Name and symbol

Europium, Eu

Atomic number

63 protons

Position

no group (f-block) · period 6 · f-block · lanthanide

CAS number

7440-53-1

Atomic structure

Atomic mass

151.964 u

Electron configuration

1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s² 4d¹⁰ 5p⁶ 6s² 4f⁷
[Xe] 6s²⁴f⁷

Electrons per shell

2, 8, 18, 25, 8, 2

Valence electrons

9 ns, (n-1)d and (n-2)f

Physical properties

State at room temperature

Solid

Melting point

1,095 K (821.85 °C)

Boiling point

1,802 K (1,528.85 °C)

Density

5.24 g/cm3

Appearance

silvery white, with a pale yellow tint; but rarely seen without oxide discoloration

Thermal conductivity

est. 13.9 W/(m·K)

Electrical resistivity

poly: 0.900 µΩ·m

Electrical conductivity

1.11 MS/m

Crystal structure

body-centered cubic

Molar heat capacity

27.66 J/(mol·K)

Chemical properties

Oxidation states

+3, +2

Electronegativity

not in sources

Ionisation energy

5.67 eV
1st 547.1, 2nd 1,085, 3rd 2,404 kJ/mol

Electron affinity

not in sources

Atomic radius

empirical 198, covalent 198, van der Waals 233 pm

Ionic radius

Eu²⁺ 117; Eu³⁺ 95 pm

Reactivity

The most reactive of the lanthanides: its half-filled 4f7 shell makes the +2 state unusually stable, so europium behaves much like calcium, tarnishing in air within hours and attacking water briskly; Eu3+ still dominates its salts.

with water

Reacts with water about as vigorously as calcium, giving the hydroxide and hydrogen: $\ce{2 Eu + 6 H2O -> 2 Eu(OH)3 + 3 H2}$, so the metal is stored under oil or argon.

with oxygen, air

Oxidises quickly in air (a centimetre piece is oxidised through in days) and ignites at 150 to $\ce{180 C: 4 Eu + 3 O2 -> 2 Eu2O3}$, the pale pink sesquioxide.

with acids

Dissolves readily in dilute sulfuric acid to pale pink Eu3+ solutions: $\ce{2 Eu + 3 H2SO4 -> Eu2(SO4)3 + 3 H2}$, with hydrogen evolved.

with halogens

Burns in the halogens to the trihalides: $\ce{2 Eu + 3 Cl2 -> 2 EuCl3}$, and the trihalides are easily reduced (by hydrogen or the metal) to divalent EuCl2.

Typical compounds

• Eu₂O₃ europium(III) oxide red phosphor in screens and lamps
• EuCl₃ europium(III) chloride soluble salt, source of Eu3+ in solution
• EuCl₂ europium(II) chloride divalent halide, made by reducing EuCl3 with hydrogen
• Eu₂(SO₄)₃ europium(III) sulfate soluble salt from the metal and sulfuric acid
• Eu(NO₃)₃ europium(III) nitrate soluble salt used to make doped phosphors

Occurrence, production and use

Crustal abundance

2.0 milligrams per kilogram

Oceanic abundance

1.3×10-7 milligrams per liter

Occurrence and sources

Europium has been identified spectroscopically in the sun and certain stars. Seventeen isotopes are now recognized. Europium isotopes are good neutron absorbers and are being studied for use in nuclear control applications.

• monazite (phosphate) and bastnaesite (fluorocarbonate) the main minerals, with the other lanthanides, in heavy-mineral sands and carbonatite deposits

Extraction, production

Ion exchange and solvent extraction from monazite and bastnaesite to europium oxide

europium oxide 99.99 percent averaged 27 dollars per kilogram in 2024 (usgs-mcs2025, PDF p148, printed p144)

Europium metal by heating europium(III) oxide with an excess of lanthanum under vacuum

$\ce{Eu2O3 + 2 La -> 2 Eu + La2O3}$

no balanced equation printed by the source

Uses

Europium is the most reactive of the rare earth elements. There are no commercial applications for europium metal, although it has been used to dope some types of plastics to make lasers. Since it is a good absorber of neutrons, europium is being studied for use in nuclear reactors.

Europium oxide (Eu2O3), one of europium's compounds, is widely used as a red phosphor in television sets and as an activator for yttrium-based phosphors.

Europium-doped plastic has been used as a laser material. With the development of ion-exchange techniques and special processes, the cost of the metal has been greatly reduced in recent years.

• Lighting, displays and security printing: red phosphor in euro banknotes that glows under ultraviolet light to reveal forgeries; red-emitting phosphor in low-energy light bulbs limited quantities of rare earths were recovered from fluorescent lamps in the United States in 2024 (usgs-mcs2025)
• Nuclear: neutron absorber in reactor control rods
• Lasers and superconductors: europium-doped plastic as a laser material; thin superconducting alloys
• Rare earth mining and separation: mined as bastnaesite (a rare-earth fluorocarbonate) at Mountain Pass, California, and as monazite (a phosphate) in heavy-mineral-sand concentrates; separated from the other rare earths by ion exchange and solvent extraction world mine production of rare earths 390,000 t of rare-earth-oxide equivalent in 2024 (USGS estimate), of which China 270,000 t (production quota), the United States 45,000 t, Burma 31,000 t, Australia, Nigeria and Thailand 13,000 t each; reserves over 90 million t, China 44 million t, Brazil 21 million t (usgs-mcs2025, PDF p149, printed p145)

Safety, toxicity

GHS classification, signal word Danger

• H228 Flammable solid Flammable solids
• H250 Catches fire spontaneously if exposed to air Pyrophoric liquids
• H260 In contact with water releases flammable gases which may ignite spontaneously Substances and mixtures which in contact with water, emit flammable gases

Discovery and name

Discovered by

Eugène-Anatole Demarçay

Discovered

1896

First isolated

not in sources

Named by

not in sources

Origin of the name

after Europe

As with other rare-earth metals, except for lanthanum, europium ignites in air at about 150 to 180°C. Europium is about as hard as lead and is quite ductile. It is the most reactive of the rare-earth metals, quickly oxidizing in air. It resembles calcium in its reaction with water. Bastnasite and monazite are the principal ores containing europium.