Cerium

Typical wastewaters

• phosphate fertiliser manufacture (phosphogypsum slurry) Ce³⁺ precipitating as fluoride and phosphate near the outfall; the largest REE tonnage 136 t of Ce to the Rhine estuary in 1994 from one plant; sediment near the outfall 170 ppm
• semiconductor manufacture (chemical mechanical polishing of silicon dioxide) cerium oxide abrasive particles of 99 to 279 nm in the slurry effluent a fixed abrasive polish produced 94 percent less CeO₂ per SiO₂ removed
• municipal sewage (engineered cerium oxide nanoparticles) CeO₂ nanoparticles, mostly adhering to sludge; surfactant stabilised particles below 200 nm leave with the effluent at a modelled 0.01 to 1 µg/L 1 to 10 µg/kg in dry biosolids (model estimate)
• mine drainage (coal) Ce³⁺ and the CeSO₄⁺ ion pair in acid sulfate water; total REE averaged 282 µg/L over 141 sites

1 · Identity

Symbol, number

Ce, 58

Oxidation states in water

+3 (Ce³⁺, dissolved, the state of all the other lanthanides) and +4 (CeO₂ and hydrous Ce(IV) oxide, solid; formed by oxidation on manganese oxide surfaces in oxic water)

Note

Ce(III) hydroxide is many orders of magnitude more soluble than Ce(IV) hydroxide (Dahle and Arai), which is why oxidation removes cerium from seawater and why acid dissolves every lanthanide oxide except CeO₂.

2 · Occurrence in water

Natural sources

The most abundant rare earth in rock and the most abundant in reducing and acid water; in oxic seawater it is depleted relative to its neighbours because Ce(III) is oxidised to insoluble Ce(IV) and scavenged (Ce anomaly 0.39 at the surface, 0.19 in deep water). Acid groundwater can show positive Ce anomalies (1.48 to 3.2) where earlier CeO₂ precipitates redissolve with Fe(II) and Mn(II).

Anthropogenic sources

Phosphogypsum discharge: 136 t of Ce entered the Rhine estuary in 1994 from one phosphate fertiliser plant, the largest of the REE tonnages, and sediment near the outfall reached 170 ppm Ce; cerium oxide polishing slurries (chemical mechanical planarisation of silicon dioxide, 99 to 279 nm ceria particles in the effluent); catalyst and fuel additive manufacture; wastewater of ceramic plants; sewage sludge. Fission product Ce-144 is among the radionuclides whose food chain concentrations near Sellafield are modelled rather than measured (RIFE 18).

3 · Speciation

Trivalent Ce³⁺ 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 CeSO₄⁺ 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 CeCO₃⁺ and Ce(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. Cerium alone adds a redox step: in oxic water Ce³⁺ is oxidised to Ce(IV), which hydrolyses and precipitates as hydrous CeO₂; in reducing or acid water it returns to Ce³⁺ (the manganese oxide surface catalysis usually invoked for the oxidation is standard geochemistry not read this session).

Solubility

Ce(III) hydroxide is many orders of magnitude more soluble than Ce(IV) hydroxide, and even Ce(III) hydroxide is not regarded as particularly soluble; chloride and nitrate are the soluble salts (Dahle and Arai, Table 2). The RIVM report puts total dissolved cerium in Dutch surface water at about 1 µg/L or less.

Hydrolysis

Hydrolysis of Ce³⁺ is minor in natural water; the hydroxide Ce(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

CeO₂ and hydrous Ce(IV) oxide (oxic); CePO₄ (hydrated), Ce₂(CO₃)₃, CeF₃ near phosphogypsum outfalls; Ce(OH)₃ under lime.

4 · Role in treatment

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 cerium anomaly is computed from shale-normalised Ce against interpolated La and Pr. Nanoparticulate ceria needs single particle ICP-MS or a centrifugation step to separate free particles from sludge bound ones.

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. Cerium salts were used as antiseptics on burns; soluble Ce(III) is more toxic to soil microbes than CeO₂ nanoparticles at equal total cerium (Dahle and Arai). CeO₂ nanoparticles act as antioxidant or as reactive oxygen species generator depending on the Ce(III) to Ce(IV) ratio, and the reports on their toxicity contradict one another.

Bioaccumulation

Field bioconcentration factors in Rhine estuary amphipods fall from the light to the heavy lanthanides (La 28,840 to Lu 4,786; Ce 48,978); 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

RIVM (2000) environmental risk limits, not discharge limits: MPC 22.1 µg/L in fresh surface water and 0.28 µg/L in salt water (negligible concentrations 0.35 and 0.13 µg/L), derived as lowest LC₅₀ divided by 1000 for both fresh and salt water plus a background set at the detection limit (0.13 µg/L). Acute data behind it: Daphnia magna 48 h EC₅₀ 22 mg/L, zebrafish 96 h LC₅₀ 22 mg/L; chronic: no chronic test listed. Field bioconcentration factor in amphipods (porewater basis) 48,978. For CeO₂ nanoparticles an early study saw no acute toxicity to Daphnia magna and Thamnocephalus platyurus up to 5000 mg/L, later ones saw effects on Daphnia swimming at 1 to 100 mg/L; E. coli viability halved at 5 mg/L (Dahle and Arai).

Flags

• The Ce oxidation equation is an electron balance written here; the cerium sources describe the oxidation but do not print it.
• Manganese oxide surface catalysis of the cerium oxidation is standard geochemistry but was not read in a source this session.
• The 0.01 to 1 µg/L effluent figure for ceria nanoparticles is a model estimate for one region.
• Phosphogypsum tonnages are 1994 data for plants that have since changed or stopped production.
• The RIVM MPC (22.1 µg/L fresh, 0.28 µg/L salt) is an environmental risk limit, LC₅₀ divided by 1000, not a permit limit.
• The Limbach paper names its surfactant suppliers; they are not written here.

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 cerium concentration in the Rhine or in groundwater was read as a per-element figure; the Rhine estuary value is for pore water.
• Cerium(IV) as an oxidant or coagulant in water treatment was not described by any source read.
• Ce-144 discharge quantities were not read; RIFE 18 only shows the nuclide in its food chain model list.

Sources

Identity

Name and symbol

Cerium, Ce

Atomic number

58 protons

Position

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

CAS number

7440-45-1

Atomic structure

Atomic mass

140.116 u

Electron configuration

1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s² 4d¹⁰ 5p⁶ 6s² 5d¹ 4f¹
[Xe] 6s²⁴f¹⁵d¹

Electrons per shell

2, 8, 18, 19, 9, 2

Valence electrons

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

Physical properties

State at room temperature

Solid

Melting point

1,071 K (797.85 °C)

Boiling point

3,697 K (3,423.85 °C)

Density

6.77 g/cm3

Appearance

silvery white

Thermal conductivity

11.3 W/(m·K)

Electrical resistivity

β-Ce, poly: 828 nΩ·m

Electrical conductivity

1.21 MS/m

Crystal structure

double hexagonal close packed

Molar heat capacity

26.94 J/(mol·K)

Chemical properties

Oxidation states

+4, +3

Electronegativity

1.12 (Pauling Scale)

Ionisation energy

5.539 eV
1st 534.4, 2nd 1,050, 3rd 1,949 kJ/mol

Electron affinity

0.5 eV

Atomic radius

empirical 204, covalent 204, van der Waals 235 pm

Ionic radius

Ce³⁺ 101; Ce⁴⁺ 87 pm

Reactivity

Except for europium the most reactive of the rare-earth metals, and unusual among them in having an accessible +4 state: it oxidises readily in moist air, may ignite when scratched, and is attacked rapidly by water, acids and alkalis.

with water

Decomposes slowly in cold water and rapidly in hot water to cerium(III) hydroxide and hydrogen: $\ce{2 Ce + 6 H2O -> 2 Ce(OH)3 + 3 H2}$.

with oxygen, air

Tarnishes readily at room temperature, especially in moist air, and the pyrophoric metal burns to the dioxide: $\ce{Ce + O2 -> CeO2}$.

with acids

Attacked rapidly by dilute and concentrated acids and by alkali solutions; dilute sulfuric acid gives Ce3+ salts and hydrogen: $\ce{2 Ce + 3 H2SO4 -> 2 Ce^3+ + 3 SO4^2- + 3 H2}$.

with halogens

Combines with the halogens on heating to the trihalides: $\ce{2 Ce + 3 Cl2 -> 2 CeCl3}$; the tetrafluoride CeF4 is also known.

Typical compounds

• CeO₂ cerium(IV) oxide ceria; glass polishing, catalytic converters, self-cleaning ovens
• Ce₂O₃ cerium(III) oxide from reducing ceria with hydrogen
• CeCl₃ cerium(III) chloride electrolysed molten for the metal
• CeF₃ cerium(III) fluoride reduced with calcium for high-purity metal
• (NH₄)₂Ce(NO₃)₆ ceric ammonium nitrate Ce(IV) laboratory oxidant and titration standard
• Ce₂S₃ cerium(III) sulfide non-toxic red pigment

Occurrence, production and use

Crustal abundance

6.65×101 milligrams per kilogram

Oceanic abundance

1.2×10-6 milligrams per liter

Occurrence and sources

Cerium is the most abundant so-called rare-earth metals. It is found in a number of minerals including allanite (also known as orthite), monazite, bastnasite, cerite, and samarskite. Monazite and bastnasite are presently the more important sources of cerium.

Large deposits of monazite (found on the beaches of Travancore, India and in river sands in Brazil), allanite (in the western United States), and bastnasite (in Southern California) will supply cerium, thorium, and the other rare-earth metals for many years to come.

Metallic cerium is prepared by metallothermic reduction techniques, such as reducing cerous fluoride with calcium, or using electrolysis of molten cerous chloride or others processes. The metallothermic technique produces high-purity cerium.

• bastnaesite, a rare earth fluorocarbonate the most common cerium mineral; mined as a primary product at Mountain Pass, California
• monazite, a rare earth phosphate heavy-mineral-sand concentrates; the world's primary thorium source as well
• cerite, a cerium silicate the historical mineral of discovery from Vestmanland, Sweden
• rare earth metals (mainly lanthanum, cerium, praseodymium, neodymium) carried with phosphate rock into wet-process phosphoric acid and discharged with phosphogypsum reported emission to water on disposal of phosphogypsum: 2,200 g and 360 g of rare earth metals per tonne P2O5 at two plants (HDH-1 and HDH-2 processes, 1996/97 data, plants since closed because of the discharge to sea); Table 5.8 of the LVIC-AAF BREF, PDF p253, printed p225; the ledger's chemical chapter holds this under the phosphoric-acid hub

Extraction, production

Cerium oxide by heating bastnaesite ore and treating with hydrochloric acid

no balanced equation printed by the source

Cerium metal by heating cerium(III) fluoride with calcium, or by electrolysis of molten cerium oxide

$\ce{2 CeF3 + 3 Ca -> 2 Ce + 3 CaF2}$

stoichiometry not printed, so no equation is written

Uses

Pure cerium will ignite if it is scratched with a sharp object, but can be safely used if combined with other materials. Cerium is one of the rare earth elements used to make carbon arc lights which are used in the motion picture industry for studio lighting and projector lights. Cerium is also a component of Misch metal, a material that is used to make flints for lighters. Cerium is also used as a catalyst to refine petroleum and as an alloying agent to make special metals.

Cerium oxide (Ce2O3 and CeO2) is a component of the walls of self cleaning ovens and of incandescent lantern mantles. Cerium oxide is also used to polish glass surfaces. Ceric sulfate (Ce(So4)2) is used in some chemical analysis processes. Other cerium compounds are used to make some types of glass as well as to remove color from glass.

Cerium is a component of misch metal, which is extensively used in the manufacture of pyrophoric alloys for cigarette lighters. While cerium is not radioactive, the impure commercial grade may contain traces of thorium, which is radioactive. The oxide is an important constituent of incandescent gas mantles and is emerging as a hydrocarbon catalyst in self cleaning ovens where it can be incorporated into oven walls to prevent the collection of cooking residues.

As ceric sulfate is used extensively as a volumetric oxidizing agent in quantitative analysis. Cerium compounds are used in the manufacture of glass, both as a component and as a decolorizer.

The oxide is finding increased use as a glass polishing agent instead of rouge, for it polishes much faster than rouge. Cerium, with other rare earths, is used in carbon-arc lighting, especially in the motion picture industry. It is also useful as a catalyst in petroleum refining and in metallurgical and nuclear applications.

• Catalysts and emission control: cerium(III) oxide as a catalyst in automotive catalytic converters; cerium oxide coatings inside self-cleaning ovens; cerium oxide nanoparticles under study as a diesel fuel additive for more complete combustion catalysts were the estimated leading United States end use of rare earths in 2024 (usgs-mcs2025, PDF p148, printed p144)
• Steel and metallurgy: mischmetal (just under 50 percent cerium) for lighter flints and pyrophoric alloys mischmetal (65 percent cerium, 35 percent lanthanum) averaged about 5 dollars per kilogram in 2024 (usgs-mcs2025)
• Glass, ceramics and pigments: cerium sulfide as a rich red, non-toxic pigment; polishing (a United States rare earth end use; the source does not name cerium for it) polishing and ceramics and glass were among the United States end uses of rare earths in 2024 (usgs-mcs2025)
• Lighting and displays: flat-screen televisions; low-energy light bulbs and floodlights
• 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
• H302 Harmful if swallowed Acute toxicity, oral
• H312 Harmful in contact with skin Acute toxicity, dermal
• H261 In contact with water releases flammable gas Substances and mixtures which in contact with water, emit flammable gases
• H370 Causes damage to organs Specific target organ toxicity, single exposure

Discovery and name

Discovered by

Martin Heinrich Klaproth, Wilhelm Hisinger, Jöns Jakob Berzelius

Discovered

1803

First isolated

William Francis Hillebrand

Named by

not in sources

Origin of the name

after dwarf planet Ceres, itself named after Roman deity of agriculture Ceres

Cerium is especially interesting because of its variable electronic structure. The energy of the inner 4f level is nearly the same as that of the outer (valence) electrons, and only small amounts of energy are required to change the relative occupancy of these electronic levels. This gives rise to dual valency states.

For example, a volume change of about 10 percent occurs when cerium is subjected to high pressures or low temperatures. Cesium's valence appears to change from about 3 to 4 when it is cooled or compressed. The low temperature behavior of cerium is complex.

Cerium is an iron-gray lustrous metal. It is malleable, and oxidizes very readily at room temperature, especially in moist air. Except for europium, cerium is the most reactive of the rare-earth metals. It decomposes slowly in cold water and rapidly in hot water.

Alkali solutions and dilute and concentrated acids attack the metal rapidly. The pure metal is likely to ignite if scratched with a knife.

Ceric slats are orange red or yellowish; cerous salts are usually white.