Neodymium

Typical wastewaters

• phosphate fertiliser manufacture (phosphogypsum slurry) Nd³⁺ precipitating as fluoride and phosphate near the outfall 75 t of Nd to the Rhine estuary in 1994 from one plant and 11 t from a second; sediment near the outfall 80 ppm
• mine drainage (coal) Nd³⁺ and the NdSO₄⁺ ion pair in acid sulfate water; total REE averaged 282 µg/L over 141 sites

1 · Identity

Symbol, number

Nd, 60

Oxidation states in water

+3 only (Nd³⁺)

Note

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

2 · Occurrence in water

Natural sources

Weathering of monazite and bastnaesite; the light lanthanide most often reported by geochemists, so its seawater profile (rising with depth from scavenging at the surface and release at depth) is the reference for the row: 2.62 to 26.66 pmol/kg in the Northwest Pacific, 4.45 pmol/kg in subtropical surface water and 22.70 pmol/kg at 2000 m in the mixed water region.

Anthropogenic sources

Phosphogypsum slurry: 75 t of Nd to the Rhine estuary in 1994 from one plant and 11 t from a second, sediment near the outfall 80 ppm Nd; neodymium-iron-boron magnet manufacture and recycling effluent is not described by any source read.

3 · Speciation

Trivalent Nd³⁺ 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 NdSO₄⁺ 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 NdCO₃⁺ and Nd(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 neodymium solid was read this session.

Hydrolysis

Hydrolysis of Nd³⁺ is minor in natural water; the hydroxide Nd(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

NdPO₄ (hydrated phosphate), Nd₂(CO₃)₃, NdF₃ near fluoride rich discharges, Nd(OH)₃ at high pH; co-precipitated on iron, aluminium and manganese hydroxides.

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.

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; Nd 29,512); 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 1.8 µg/L in fresh surface water and 0.86 µg/L in salt water (negligible concentrations 0.40 and 0.009 µg/L), derived as lowest LC₅₀ divided by 1000; the Daphnia EC₅₀ of 1.4 mg/L is the lowest of the eight elements tested plus a background set at the detection limit (0.39 µg/L). Acute data behind it: Daphnia magna 48 h EC₅₀ 1.4 mg/L, zebrafish 96 h LC₅₀ 21 mg/L; chronic: Daphnia magna 21 d NOEC 1.6 mg/L (mortality and reproduction). Field bioconcentration factor in amphipods (porewater basis) 29,512.

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.
• No neodymium specific river concentration was read; the Rhine estuary survey reports Nd only in sediment (80 ppm near the outfall).

Sources

Identity

Name and symbol

Neodymium, Nd

Atomic number

60 protons

Position

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

CAS number

7440-00-8

Atomic structure

Atomic mass

144.242 u

Electron configuration

1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s² 4d¹⁰ 5p⁶ 6s² 4f⁴
[Xe] 6s²⁴f⁴

Electrons per shell

2, 8, 18, 22, 8, 2

Valence electrons

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

Physical properties

State at room temperature

Solid

Melting point

1,294 K (1,020.85 °C)

Boiling point

3,347 K (3,073.85 °C)

Density

7.01 g/cm3

Appearance

silvery white

Thermal conductivity

16.5 W/(m·K)

Electrical resistivity

poly: 643 nΩ·m

Electrical conductivity

1.56 MS/m

Crystal structure

double hexagonal close packed

Molar heat capacity

27.45 J/(mol·K)

Chemical properties

Oxidation states

+3

Electronegativity

1.14 (Pauling Scale)

Ionisation energy

5.525 eV
1st 533.1, 2nd 1,040, 3rd 2,130 kJ/mol

Electron affinity

not in sources

Atomic radius

empirical 201, covalent 201, van der Waals 229 pm

Ionic radius

Nd²⁺ 129 (8-coordinate); Nd³⁺ 98 pm

Reactivity

One of the more reactive rare-earth metals: it tarnishes quickly in air to an oxide that flakes off and exposes fresh metal, reacts with water and dissolves in dilute acids, so it is stored under mineral oil or sealed in plastic.

with water

Reacts slowly with cold water and quickly with hot water to neodymium(III) hydroxide and hydrogen: $\ce{2 Nd + 6 H2O -> 2 Nd(OH)3 + 3 H2}$.

with oxygen, air

Tarnishes quickly in air, the oxide spalling off to expose fresh metal; at about 150 C it burns to the sesquioxide: $\ce{4 Nd + 3 O2 -> 2 Nd2O3}$.

with acids

Dissolves readily in dilute sulfuric acid to lilac Nd3+ solutions and hydrogen: $\ce{2 Nd + 3 H2SO4 -> 2 Nd^3+ + 3 SO4^2- + 3 H2}$.

with halogens

Reacts vigorously with all the stable halogens to the trihalides: $\ce{2 Nd + 3 Cl2 -> 2 NdCl3}$, mauve; the fluoride and bromide are violet, the iodide green.

Typical compounds

• Nd₂O₃ neodymium(III) oxide violet glass colourant, polymerisation catalyst
• NdCl₃ neodymium(III) chloride mauve trihalide
• NdF₃ neodymium(III) fluoride violet trihalide
• Nd₂Fe₁₄B neodymium iron boron the strongest permanent magnets; motors, turbines, phones
• Nd(NO₃)₃ neodymium(III) nitrate soluble salt; polymerisation catalyst

Occurrence, production and use

Crustal abundance

4.15×101 milligrams per kilogram

Oceanic abundance

2.8×10-6 milligrams per liter

Occurrence and sources

• monazite (phosphate) and bastnaesite (fluorocarbonate) the main sources of most lanthanides; heavy-mineral sands and the Mountain Pass carbonatite deposit
• 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

Ion exchange and solvent extraction from monazite and bastnaesite to neodymium (or neodymium-praseodymium) oxide

neodymium oxide 99.5 percent averaged 56 dollars per kilogram in 2024 (usgs-mcs2025, PDF p148, printed p144)

Reduction of anhydrous neodymium chloride or fluoride with calcium to the metal

$\ce{2 NdCl3 + 3 Ca -> 2 Nd + 3 CaCl2}$

no balanced equation printed by the source

Uses

Neodymium makes up about 18% of Misch metal, a material that is used to make flints for lighters. Neodymium is also a component of didymium glass, which is used to make certain types of welder's and glass blower's goggles. Neodymium is added to glass to remove the green color caused by iron contaminants. It can also be added to glass to create violet, red or gray colors. Some types of glass containing neodymium are used by astronomers to calibrate devices called spectrometers and other types are used to create artificial rubies for lasers. Some neodymium salts are used to color enamels and glazes.

Didymium, of which neodymium is a component, is used for coloring glass to make welders goggles. By itself, neodymium colors glass delicate shades ranging from pure violet through wine-red and warm gray. Light transmitted through such glass shows unusually sharp absorption bands. The glass has been used in astronomical work to produce sharp bands by which spectral lines may be calibrated. Glass containing neodymium can be used as a laser material to produce coherent light. Neodymium salts are also used as a colorant for enamels.

• Permanent magnets: neodymium-iron-boron magnets in mobile phones, microphones, loudspeakers and electronic musical instruments; motors and generators in windscreen wipers, electric vehicles and wind turbines neodymium-iron-boron magnet block is a potential United States stockpile acquisition for fiscal years 2024 and 2025; significant amounts of rare earths enter the United States as magnets embedded in finished goods (usgs-mcs2025, PDF p148 to 149, printed p144 to 145)
• Glass and lasers: didymium glass with praseodymium for welding and glass-blowing goggles; tanning-booth glass that passes ultraviolet and blocks infrared; neodymium-doped laser glass for pointers, eye and cosmetic surgery and skin cancer treatment
• Polymer catalysts: neodymium oxide and nitrate as catalysts in polymerisation reactions
• 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

Neodymium has a low-to-moderate acute toxic rating. As with other rare earths, neodymium should be handled with care.

GHS classification, signal word Danger

• H228 Flammable solid Flammable solids
• H251 Self-heating; may catch fire Self-heating substances and mixtures
• H315 Causes skin irritation Skin corrosion/irritation
• H319 Causes serious eye irritation Serious eye damage/eye irritation
• H413 May cause long lasting harmful effects to aquatic life to the aquatic environment, long-term hazard

Discovery and name

Discovered by

Carl Gustaf Mosander

Discovered

1841

First isolated

Carl Auer von Welsbach

Named by

Carl Auer von Welsbach

Origin of the name

after Greek νέος, "new", and δίδυμος, "twin" (of lanthanum)

The metal has a bright silvery metallic luster, Neodymium is one of the more reactive rare-earth metals and quickly tarnishes in air, forming an oxide that spalls off and exposes metal to oxidation. The metal, therefore, should be kept under light mineral oil or sealed in a plastic material. Neodymium exists in two allotropic forms, with a transformation from a double hexagonal to a body-centered cubic structure taking place at 863°C.