Niobium

Typical wastewaters

No sourced effluent type yet.

1 · Identity

Symbol, number

Nb, 41

Oxidation states in water

+5 only; hydrolysed niobate and hydroxo species, fluoride complexes where fluoride is present

Note

The element entry covers the corrosion resistant metal and Nb₂O₅. In water niobium behaves as a hard acid with an oxygen and fluoride affinity, like zirconium and tantalum.

2 · Occurrence in water

Natural sources

Weathering of pyrochlore and columbite releases almost nothing; dissolved niobium is a few pmol/kg in seawater and 1 to several hundred ng/L in mineral waters, highest in deep geothermal waters of volcanic areas (from the voltammetry method paper and a search summary).

Anthropogenic sources

Ferroniobium steel, superalloy and capacitor manufacture (element entry and review); niobium-95 is a fission product.

3 · Speciation

Nb(V) hydrolyses extensively even in mildly acid water and is held in oxide and hydroxo species of very low solubility; fluoride raises its solubility far above chloride, sulfate or carbonate media. The review gives no explicit species for seawater.

Solubility

Very low without fluoride.

Hydrolysis

Extensive.

Complexation

Fluoride strongly; the analytical method avoids fluoride and hydrofluoric acid for that reason.

Precipitates

Hydrous Nb₂O₅.

4 · Role in treatment

Not relevant or not given for this element.

5 · Removal and control

Not relevant or not given for this element.

6 · Analytics

Sampling pitfalls

Niobium sorbs to walls and particles and dissolves only with fluoride; acid preservation without fluoride loses it, fluoride digestion contaminates ICP-MS. The voltammetry paper notes that niobium values in natural waters carry considerable uncertainty for these reasons.

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 toxicity data were read.

Bioaccumulation

The review notes a high accumulation coefficient by zooplankton and seaweed enrichment factors of 10^5 to 10^7 for niobium and tantalum, and tantalum biomagnification in Chilean coastal food webs.

Ecotoxicity

Not read.

Flags

• The geothermal water statement and the fluoride speciation come from search summaries of papers not read.
• Mineral water concentrations are given only as a range in the abstract.

Gaps

• No river or groundwater concentration from a read source; no hydrolysis constants or solubility product read.
• No wastewater concentration and no removal process were read; none is practised.
• No ecotoxicity data were read.
• No GCC discharge standard was read.
• No sourced wastewater type for niobium: the wastewaters list is left empty because no source read describes niobium in any industrial or municipal effluent.

Sources

Identity

Name and symbol

Niobium, Nb

Atomic number

41 protons

Position

group 5 · period 5 · d-block · transition metal

CAS number

7440-03-1

Atomic structure

Atomic mass

92.906 u

Electron configuration

1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s¹ 4d⁴
[Kr] 5s¹⁴d⁴

Electrons per shell

2, 8, 18, 12, 1

Valence electrons

5 ns and (n-1)d

Physical properties

State at room temperature

Solid

Melting point

2,750 K (2,476.85 °C)

Boiling point

5,017 K (4,743.85 °C)

Density

8.57 g/cm3

Appearance

Gray metallic, bluish when oxidized

Thermal conductivity

53.7 W/(m·K)

Electrical resistivity

152 nΩ·m at 0 °C

Electrical conductivity

6.58 MS/m

Crystal structure

cubic body-centered

Molar heat capacity

24.6 J/(mol·K)

Chemical properties

Oxidation states

+5, +3

Electronegativity

1.6 (Pauling Scale)

Ionisation energy

6.759 eV
1st 652.1, 2nd 1,380, 3rd 2,416 kJ/mol

Electron affinity

0.893 eV

Atomic radius

empirical 164, covalent 164, van der Waals 207 pm

Ionic radius

Nb³⁺ 72; Nb⁴⁺ 68; Nb⁵⁺ 64 pm

Reactivity

A refractory group 5 metal that is chemically inert at room temperature because of a protective oxide film: it withstands aqua regia and most acids, and reacts with the non-metals only on heating.

with water

Does not react with water.

with oxygen, air

Takes on a bluish tinge after long exposure to air at room temperature and begins to oxidise at 200 C, ultimately to the pentoxide: $\ce{4 Nb + 5 O2 -> 2 Nb2O5}$.

with acids

Resists aqua regia and dilute hydrochloric, sulfuric, nitric and phosphoric acids; attacked by hydrofluoric acid, hydrofluoric-nitric mixtures, hot concentrated sulfuric acid and hot concentrated alkali hydroxides.

with halogens

Reacts with fluorine at room temperature and with chlorine at about 150 C to the pentahalides: $\ce{2 Nb + 5 Cl2 -> 2 NbCl5}$.

Typical compounds

• Nb₂O₅ niobium pentoxide precursor to most niobium compounds; raises glass refractive index
• NbCl₅ niobium pentachloride yellow solid, starting point for organometallics
• NbC niobium carbide very hard ceramic for cutting tools
• NbN niobium nitride low-temperature superconductor for infrared detectors
• LiNbO₃ lithium niobate niobate for optical modulators and acoustic devices
• Nb₃Sn niobium-tin superconducting wire for MRI and accelerator magnets

Occurrence, production and use

Crustal abundance

2.0×101 milligrams per kilogram

Oceanic abundance

1×10-5 milligrams per liter

Occurrence and sources

The element is found in niobite (or columbite), niobite-tantalite, parochlore, and euxenite. Large deposits of niobium have been found associated with carbonatites (carbon-silicate rocks), as a constituent of parochlore. Extensive ore reserves are found in Canada, Brazil, Nigeria, Zaire, and in Russia.

• pyrochlore in carbonatite Araxa and Catalao (Brazil), Niobec (Canada); most identified world resources
• columbite-tantalite (coltan) pegmatites in Brazil, Canada, Australia, Nigeria, Congo (Kinshasa), Rwanda, Mozambique
• by-product of tin (cassiterite) processing tin slags
• crustal and oceanic abundance about 8 ppm (BGS figure via RSC); 20 mg/kg crust and 0.00001 mg/L seawater (PubChem)

Extraction, production

Pyrochlore concentrate to ferroniobium

$\ce{3 Nb2O5 (s) + 10 Al (l) -> 6 Nb (s) + 5 Al2O3 (s)}$

Ferroniobium (about 65 percent Nb) is the traded form, 71 percent of US niobium imports by content; the aluminothermic reduction chemistry is not stated by USGS or RSC

Hydrogen reduction of niobium chloride (historical metal route)

$\ce{2 NbCl5 (g) + 5 H2 (g) -> 2 Nb (s) + 10 HCl (g)}$

RSC states Blomstrand reduced niobium chloride by heating it with hydrogen; hydrogen chloride as the co-product is implied by the reduction, not named

Uses

Niobium is used as an alloying agent and for jewelry, but perhaps its most interesting applications are in the field of superconductivity. Superconductive wire can be made from an alloy of niobium and titanium which can then be used to make superconductive magnets. Other alloys of niobium, such as those with tin and aluminum, are superconductive as well. Pure niobium is itself a superconductor when it is cooled below 9.25 K (-442.75°F). Superconductive niobium cavities are at the heart of a machine built at the Thomas Jefferson National Accelerator Facility. This machine, called an electron accelerator, is used by scientists to study the quark structure of matter. The accelerator's 338 niobium cavities are bathed in liquid helium and accelerate electrons to nearly the speed of light.

Niobium is used in arc-welding rods for stabilized grades of stainless steel. Thousands of pounds of niobium have been used in advanced air frame systems such as were used in the Gemini space program. The element has superconductive properties; superconductive magnets have been made with Nb-Zr wire, which retains its superconductivity in strong magnetic fields. This type of application offers hope of direct large-scale generation of electric power. Niobium is also commonly used for jewelry.

• Steel: ferroniobium microalloying of high-strength low-alloy and stainless steels for pipelines, structural beams, oil rigs, vehicles about 77 percent of US niobium consumption in 2024 (usgs-mcs2025-niobium)
• Aerospace superalloys: nickel-base superalloys for jet engines and rockets; high-purity niobium oxide for aerospace grades about 21 percent of US consumption in 2024 (usgs-mcs2025-niobium)
• Superconductors and medical imaging: niobium-titanium and niobium-tin magnet wire for MRI, NMR and accelerators
• Glass: niobium oxide to raise refractive index for thinner corrective lenses
• Mining: pyrochlore and columbite mining; niobium recovered as a by-product of tin extraction

Safety, toxicity

GHS classification, signal word Danger

• H228 Flammable solid Flammable solids

Discovery and name

Discovered by

Charles Hatchett

Discovered

1801

First isolated

Christian Wilhelm Blomstrand

Named by

not in sources

Origin of the name

after Niobe in Greek mythology, daughter of Tantalus (tantalum)

Niobium is a shiny, white, soft, and ductile metal, and takes on a bluish cast when exposed to air at room temperatures for a long time. The metal starts to oxidize in air at 200°C, and when processed at even moderate temperatures must be placed in a protective atmosphere.