Lutetium

Typical wastewaters

• hospital effluent (Lu-177 radiotherapy wards) Lu-177 and its long lived Lu-177m impurity from excreted radiopharmaceuticals, in ward wastewater held for decay and counted before release to the sewer 1 L samples counted at two time points; activities per patient and clearance levels not read
• rare earth separation and processing (saponification wastewater) Lu³⁺ carried with the whole lanthanide row in ammonia rich separation plant wastewater (ammonia nitrogen 300 to 5,000 mg/L in Chinese saponification wastewater, 2005 estimate) no lutetium specific concentration read
• coal mine drainage (acid) Lu³⁺ and the LuSO₄⁺ 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

Lu, 71

Oxidation states in water

+3 only (Lu³⁺)

Note

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

2 · Occurrence in water

Natural sources

Weathering of monazite and xenotime; the heaviest lanthanide, the most strongly carbonate complexed and the lowest bioconcentration factor of the row (4,786 in amphipods); the lowest concentration of the row in the Rhine estuary survey (below 0.1 ppm in North Sea sediment, below 0.001 ppb in pore water).

Anthropogenic sources

Lu-177 labelled radiopharmaceuticals excreted by patients: wastewater from therapy wards can contain Lu-177 with its Lu-177m impurity, whose half-life is much longer than I-131; some countries require storage in dedicated systems and nuclide specific verification below clearance levels before discharge to the public sewer (Kupitz 2024, 1 L samples counted in a wastewater counter at two time points). Soft drink syrup enriches Lu, Yb and Ce in post-mix beverages relative to the tap water.

3 · Speciation

Trivalent Lu³⁺ 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 LuSO₄⁺ 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 LuCO₃⁺ and Lu(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.

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 lutetium solid was read this session.

Hydrolysis

Hydrolysis of Lu³⁺ is minor in natural water; the hydroxide Lu(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

LuPO₄ (hydrated phosphate), Lu₂(CO₃)₃, LuF₃ near fluoride rich discharges, Lu(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. For Lu-177 in ward wastewater: gamma spectrometric counting of 1 L samples in a wastewater counter at two time points to separate Lu-177m from I-131.

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 chemical toxicity data for lutetium were read. The radiological question is Lu-177 and Lu-177m activity in ward wastewater, governed by national clearance levels, not by drinking water rules.

Bioaccumulation

Field bioconcentration factors in Rhine estuary amphipods fall from the light to the heavy lanthanides (La 28,840 to Lu 4,786; Lu 4,786); 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 lutetium: the RIVM report set risk limits only for Y, La, Ce, Pr, Nd, Sm, Gd and Dy. The one lutetium number it carries is a field bioconcentration factor in amphipods of 4,786 (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.

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.
• Lu-177 activities discharged per patient and national clearance levels were not read as numbers.
• No lutetium chemical toxicity test was read.

Sources

Identity

Name and symbol

Lutetium, Lu

Atomic number

71 protons

Position

group 3 · period 6 · d-block · lanthanide

CAS number

7439-94-3

Atomic structure

Atomic mass

174.966 u

Electron configuration

1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s² 4d¹⁰ 5p⁶ 6s² 4f¹⁴ 5d¹
[Xe] 6s²⁴f¹⁴⁵d¹

Electrons per shell

2, 8, 18, 32, 9, 2

Valence electrons

3 ns and (n-1)d

Physical properties

State at room temperature

Solid

Melting point

1,936 K (1,662.85 °C)

Boiling point

3,675 K (3,401.85 °C)

Density

9.84 g/cm3

Appearance

silvery white

Thermal conductivity

16.4 W/(m·K)

Electrical resistivity

poly: 582 nΩ·m

Electrical conductivity

1.72 MS/m

Crystal structure

hexagonal close packed

Molar heat capacity

26.86 J/(mol·K)

Chemical properties

Oxidation states

+3

Electronegativity

1.27 (Pauling Scale)

Ionisation energy

5.426 eV
1st 523.5, 2nd 1,340, 3rd 2,022.3 kJ/mol

Electron affinity

not in sources

Atomic radius

empirical 187, covalent 187, van der Waals 221 pm

Ionic radius

Lu³⁺ 86 pm

Reactivity

The last lanthanide (4f14 5d1 6s2), the hardest and densest of them, with a full 4f shell that leaves only the +3 state; its colourless Lu3+ salts behave like those of yttrium, and the metal resists dry air but not moist air, water or acids.

with water

Reacts with water, slowly when cold and quickly when hot, to the hydroxide and hydrogen: $\ce{2 Lu + 6 H2O -> 2 Lu(OH)3 + 3 H2}$, the hydroxide being insoluble.

with oxygen, air

Relatively stable in dry air but slightly unstable in moist air; burns readily at 150 C to the oxide: $\ce{4 Lu + 3 O2 -> 2 Lu2O3}$, which then absorbs water and carbon dioxide from the air.

with acids

Dissolves readily in weak acids and in dilute sulfuric acid to colourless Lu3+ solutions with evolution of hydrogen: $\ce{2 Lu + 3 H2SO4 -> Lu2(SO4)3 + 3 H2}$, the sulfate.

with halogens

Reacts with the four lightest halogens to the trihalides: $\ce{2 Lu + 3 Cl2 -> 2 LuCl3}$, all soluble in water except the fluoride.

Typical compounds

• Lu₂O₃ lutetium(III) oxide lutetia, white insoluble oxide, absorbs water and carbon dioxide
• LuCl₃ lutetium(III) chloride anhydrous chloride reduced with an alkali metal to lutetium
• LuF₃ lutetium(III) fluoride the one water-insoluble trihalide, also a metal precursor
• LuI₃ lutetium(III) iodide brown, the one coloured simple salt
• Lu₂(SO₄)₃ lutetium(III) sulfate colourless soluble salt, crystallises as a hydrate

Occurrence, production and use

Crustal abundance

8×10-1 milligrams per kilogram

Oceanic abundance

1.5×10-7 milligrams per liter

Occurrence and sources

• monazite the main source, with the other lanthanides

Extraction, production

Reduction of anhydrous lutetium fluoride with calcium metal

$\ce{2 LuF3 + 3 Ca -> 2 Lu + 3 CaF2}$

extracted with difficulty; no equation printed

Uses

Lutetium is one of the most difficult elements to prepare and has no large scale practical uses, although some of its radioactive isotopes can be used as a catalyst in the cracking of petroleum products and a catalyst in some hydrogenation and polymerization processes.

Stable lutetium nuclides, which emit pure beta radiation after thermal neutron activation, can be used as catalysts in cracking, alkylation, hydrogenation, and polymerization. Virtually no other commercial uses have been found yet for lutetium.

Safety, toxicity

While lutetium, like other rare-earth metals, is thought to have a low toxicity rating, it should be handled with care until more information is available.

GHS classification, signal word Danger

• H228 Flammable solid Flammable solids

Discovery and name

Discovered by

Carl Auer von Welsbach and Georges Urbain

Discovered

1906

First isolated

not in sources

Named by

Georges Urbain

Origin of the name

after Lutetia, Latin for: Paris, in the Roman era

Lutetium occurs in very small amounts in nearly all minerals containing yttrium, and is present in monazite to the extent of about 0.003%, which is a commercial source. The pure metal has been isolated only in recent years and is one of the most difficult to prepare. It can be prepared by the reduction of anhydrous LuCl3 or LuF3 by an alkali or alkaline earth metal. The metal is silvery white and relatively stable in air. 176Lu occurs naturally (2.6%) with 175Lu (97.4%). It is radioactive with a half-life of about 3 x 1010 years.