Samarium

Typical wastewaters

• refinery catalyst manufacture (fluid catalytic cracking catalyst plant effluent) water soluble anthropogenic samarium, partly bound to colloids and nanoparticles between 10 kDa and 0.2 µm, in a river matrix; 84 to 87 percent of dissolved Sm at Leverkusen the Rhine point source north of Worms; up to 584 kg a year to the North Sea
• phosphate fertiliser manufacture (phosphogypsum slurry) Sm³⁺ in phosphogypsum slurry discharged to the Rhine estuary, 15 t of Sm in 1994, 20 ppm Sm in sediment near the outfall
• coal mine drainage (acid) Sm³⁺ and the SmSO₄⁺ 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

1 · Identity

Symbol, number

Sm, 62

Oxidation states in water

+3 only (Sm³⁺)

Note

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

2 · Occurrence in water

Natural sources

Weathering of monazite and bastnaesite; a middle lanthanide between the light and heavy halves of the row.

Anthropogenic sources

Fluid catalytic cracking catalyst plant effluent on the Rhine north of Worms (river-km 447.3): anthropogenic Sm 5.0 to 7.3 ng/kg at Leverkusen on a geogenic background of 0.96 to 1.1 ng/kg (84 to 87 percent anthropogenic), 3.1 ng/kg (37 percent) still at Leerdam in the Netherlands 500 km downstream, up to 584 kg a year toward the North Sea; phosphogypsum slurry, 15 t of Sm to the Rhine estuary in 1994, sediment near the outfall 20 ppm Sm. Sm-153 is a therapeutic radionuclide (the thesis notes its medical use; no wastewater measurement read).

3 · Speciation

Trivalent Sm³⁺ 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 SmSO₄⁺ 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 SmCO₃⁺ and Sm(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. Unlike anthropogenic gadolinium, which stays in the truly dissolved pool below 10 kDa, the anthropogenic samarium and lanthanum of the Rhine are partly bound to colloids and nanoparticles between 10 kDa and 0.2 µm, and anthropogenic Sm and La are taken up into freshwater mussel shells while anthropogenic Gd is not.

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 samarium solid was read this session.

Hydrolysis

Hydrolysis of Sm³⁺ is minor in natural water; the hydroxide Sm(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

SmPO₄ (hydrated phosphate), Sm₂(CO₃)₃, SmF₃ near fluoride rich discharges, Sm(OH)₃ at high pH; co-precipitated on iron, aluminium and manganese hydroxides.

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 Rhine work used Eu to quantify the anthropogenic Sm input (Gd being contaminated itself), while noting that Eu's 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 anywhere read; no acute or chronic human toxicity data for this element 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; Sm 17,783); 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 8.2 µg/L in fresh surface water and 0.42 µg/L in salt water (negligible concentrations 0.64 and 0.005 µg/L), derived as lowest LC₅₀ divided by 1000 plus a background set at the detection limit (0.56 µg/L). Acute data behind it: Daphnia magna 48 h EC₅₀ 7.6 mg/L, zebrafish 96 h LC₅₀ 22 mg/L; chronic: no chronic test listed. Field bioconcentration factor in amphipods (porewater basis) 17,783. Anthropogenic Sm is bioavailable to the mussel Corbicula fluminea.

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.
• Rhine samarium figures are single campaigns from one river with a point source.

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 Sm-153 hospital wastewater measurement was read.

Sources

Identity

Name and symbol

Samarium, Sm

Atomic number

62 protons

Position

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

CAS number

7440-19-9

Atomic structure

Atomic mass

150.36 u

Electron configuration

1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s² 4d¹⁰ 5p⁶ 6s² 4f⁶
[Xe] 6s²⁴f⁶

Electrons per shell

2, 8, 18, 24, 8, 2

Valence electrons

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

Physical properties

State at room temperature

Solid

Melting point

1,347 K (1,073.85 °C)

Boiling point

2,067 K (1,793.85 °C)

Density

7.52 g/cm3

Appearance

silvery white

Thermal conductivity

13.3 W/(m·K)

Electrical resistivity

α, poly: 0.940 (at r.t.) µΩ·m

Electrical conductivity

1.06 MS/m

Crystal structure

rhombohedral

Molar heat capacity

29.54 J/(mol·K)

Chemical properties

Oxidation states

+3, +2

Electronegativity

1.17 (Pauling Scale)

Ionisation energy

5.644 eV
1st 544.5, 2nd 1,070, 3rd 2,260 kJ/mol

Electron affinity

not in sources

Atomic radius

empirical 198, covalent 198, van der Waals 229 pm

Ionic radius

Sm²⁺ 122 (7-coordinate); Sm³⁺ 96 pm

Reactivity

A typical electropositive lanthanide whose chemistry is dominated by Sm3+ (4f5), but one of the three lanthanides (with Eu and Yb) with an easily reached +2 state; the metal is reasonably stable in dry air but is a strong reducing agent.

with water

Reacts slowly with cold water and rapidly with hot water to the hydroxide and hydrogen: $\ce{2 Sm + 6 H2O -> 2 Sm(OH)3 + 3 H2}$, the hydroxide is a white solid.

with oxygen, air

Oxidises slowly in air at room temperature (a grey-yellow oxide crust grows even under oil) and ignites at about $\ce{150 C: 4 Sm + 3 O2 -> 2 Sm2O3}$, the sesquioxide.

with acids

Dissolves readily in dilute sulfuric acid to yellow-green Sm3+ solutions: $\ce{2 Sm + 3 H2SO4 -> Sm2(SO4)3 + 3 H2}$, with hydrogen evolved.

with halogens

Reacts with all the halogens on heating to the trihalides: $\ce{2 Sm + 3 Cl2 -> 2 SmCl3}$, while reduction of the triiodide gives the divalent SmI2.

Typical compounds

• Sm₂O₃ samarium(III) oxide infrared-absorbing glass additive and ethanol dehydrogenation catalyst
• SmCl₃ samarium(III) chloride starting point for organosamarium chemistry
• SmI₂ samarium(II) iodide blood-red one-electron reducing agent in organic synthesis
• Sm₂(SO₄)₃ samarium(III) sulfate salt formed when the metal dissolves in sulfuric acid
• SmCo₅ samarium cobalt intermetallic permanent magnet, highest known coercivity

Occurrence, production and use

Crustal abundance

7.05 milligrams per kilogram

Oceanic abundance

4.5×10-7 milligrams per liter

Occurrence and sources

Samarium is found along with other members of the rare-earth elements in many minerals, including monazite and bastnasite, which are commercial sources. It occurs in monazite to the extent of 2.8%. While misch metal containing about 1% of samarium metal, has long been used, samarium has not been isolated in relatively pure form until recently. Ion-exchange and solvent extraction techniques have recently simplified separation of the rare earths from one another; more recently, electrochemical deposition, using an electrolytic solution of lithium citrate and a mercury electrode, is said to be a simple, fast, and highly specific way to separate the rare earths. Samarium metal can be produced by reducing the oxide with lanthanum.

• monazite (phosphate) and bastnaesite (fluorocarbonate) the principal minerals, with the other lanthanides; samarskite is the historical mineral of discovery

Extraction, production

Separation from the other lanthanides by ion exchange and solvent extraction; electrochemical deposition from a lithium citrate electrolyte onto a mercury electrode has also been used

no balanced equation printed by the source

Reduction of samarium oxide with barium to the metal

$\ce{Sm2O3 + 3 Ba -> 2 Sm + 3 BaO}$

stoichiometry not printed, so no equation is written

Uses

Samarium 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. Samarium also makes up about 1% of Misch metal, a material that is used to make flints for lighters.

Samarium forms a compound with cobalt (SmCo5) which is a powerful permanent magnet with the highest resistance to demagnetization of any material known. Samarium oxide (Sm2O3) is added to glass to absorb infrared radiation and acts as a catalyst for the dehydration and dehydrogenation of ethanol (C2H6O).

Samarium, along with other rare earths, is used for carbon-arc lighting for the motion picture industry. SmCo5 has been used in making a new permanent magnet material with the highest resistance to demagnetization of any known material. It is said to have an intrinsic coercive force as high as 2200 kA/m. Samarium oxide has been used in optical glass to absorb the infrared. Samarium is used to dope calcium fluoride crystal for use in optical lasers or lasers. Compounds of the metal act as sensitizers for phosphors excited in the infrared; the oxide exhibits catalytic properties in the dehydration and dehydrogenation of ethyl alcohol. It is used in infrared absorbing glass and as a neutron absorber in nuclear reactors.

• Permanent magnets: samarium-cobalt magnets for high-temperature and microwave applications; historically the magnets that miniaturised headphones and personal stereos, now largely replaced by neodymium magnets samarium-cobalt alloy is a potential United States stockpile acquisition for fiscal years 2024 and 2025 (usgs-mcs2025, PDF p149, printed p145)
• Nuclear: neutron absorber in nuclear reactors
• Glass, ceramics and lasers: dopant for calcium chloride crystals in optical lasers; infrared-absorbing glass; samarium oxide in specialised glass and ceramics; carbon arc lighting for studios and projection
• 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

Little is known of the toxicity of samarium; therefore, it should be handled carefully.

GHS classification, signal word Danger

• H228 Flammable solid Flammable solids
• H261 In contact with water releases flammable gas Substances and mixtures which in contact with water, emit flammable gases

Discovery and name

Discovered by

Lecoq de Boisbaudran

Discovered

1879

First isolated

Wilhelm Muthmann

Named by

not in sources

Origin of the name

after the mineral samarskite (itself named after Vassili Samarsky-Bykhovets)

Samarium has a bright silver luster and is reasonably stable in air. Three crystal modifications of the metal exist, with transformations at 734 and 922°C. The metal ignites in air at about 150°C. The sulfide has excellent high-temperature stability and good thermoelectric efficiencies up to 1100°C.