Tungsten

Typical wastewaters

• tungsten mining and tailings
  tungstate WO₄²⁻ in tailings groundwater, up to 922 mg/L at the Yxsjoberg skarn tailings in Sweden; precipitates with calcium as scheelite where calcium is high
• hard metal and tungsten carbide manufacture
  tungstate at hundreds of mg/L in hard metal and tungsten chemical effluents
  ferric coagulation at acid pH is the industrial removal route
• semiconductor fabrication
  tungstate remaining at 400 µg/L in treated effluent from a Taiwanese science park

1 · Identity

Symbol, number

W, 74

Oxidation states in water

+6 as the tungstate anion WO₄²⁻, the form in neutral and alkaline water; at lower pH tungstate polymerises to isopolytungstates (ATSDR); the metal and lower oxides are insoluble solids.

Note

The element chapter covers the metal, scheelite and wolframite. In water tungsten is a molybdate like oxyanion, mobile in alkaline sodium bicarbonate water and sorbed in acid water.

2 · Occurrence in water

Natural sources

Weathering of tungsten mineral deposits and geothermal waters; Fallon, Nevada, municipal supplies had a mean of 19.1 µg/L (range 0.25 to 27.2) and private wells 37.5 µg/L (0.25 to 337); Icelandic groundwaters 0.03 to 11.5 µg/L and surface waters 0.015 to 0.49 µg/L in areas of natural tungsten mineralisation (ATSDR 2005).

Anthropogenic sources

Tungsten mining and tailings (groundwater in the Yxsjoberg skarn tailings in Sweden reached 922 mg/L), hard metal and tungsten carbide manufacture, semiconductor fabrication (treated wastewater from a Taiwanese science park still at 400 µg/L), tungsten ammunition at shooting ranges (pore water 1 to 400 mg/L) (Yang 2022); rainwater near a Russian hard metal factory 0.00014 and 0.00076 µg/L in solid and soluble phases (ATSDR).

3 · Speciation

Tungstate WO₄²⁻ is the dissolved species in neutral and alkaline water; sorption to iron and manganese minerals increases as pH falls and tungstate polymerises to isopolytungstates at lower pH (ATSDR). Calcium precipitates it as scheelite CaWO₄ when concentrations are high (above about 5 mmol/L in the hydrocalumite study, Yang 2022).

Solubility

Scheelite is the sparingly soluble calcium salt; sodium tungstate is freely soluble. No solubility product read.

Hydrolysis

Tungstic acid H₂WO₄ forms and polymerises below about pH 6; not quantified in the sources read.

Complexation

Polytungstates with itself; sorption complexes on Fe and Mn oxides.

Precipitates

CaWO₄ scheelite; FeWO₄ and MnWO₄ (wolframite) in the ore; tungstate co-precipitated on ferric hydroxide.

4 · Role in treatment

5 · Removal and control

6 · Analytics

Sampling pitfalls

Do not acidify strongly: tungstate polymerises and sorbs to walls and particles below pH 6; keep samples near neutral or slightly alkaline and filter first.

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

ATSDR (2005) found the human data too limited for health guidance; no drinking water value exists in any body read.

Bioaccumulation

not relevant

Ecotoxicity

Elevated tungsten may inhibit ammonification and nitrification in surface waters (ATSDR); no aquatic criterion exists.

Identity

Name and symbol

Tungsten, W

Atomic number

74 protons

Position

group 6 · period 6 · d-block · transition metal

CAS number

7440-33-7

Atomic structure

Atomic mass

183.84 u

Electron configuration

1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s² 4d¹⁰ 5p⁶ 6s² 4f¹⁴ 5d⁴
[Xe] 6s²⁴f¹⁴⁵d⁴

Electrons per shell

2, 8, 18, 32, 12, 2

Valence electrons

6 ns and (n-1)d

Physical properties

State at room temperature

Solid

Melting point

3,695 K (3,421.85 °C)

Boiling point

5,828 K (5,554.85 °C)

Density

19.3 g/cm3

Appearance

Grayish white, lustrous

Thermal conductivity

173 W/(m·K)

Electrical resistivity

52.8 nΩ·m at 20 °C

Electrical conductivity

18.94 MS/m

Crystal structure

body-centered cubic

Molar heat capacity

24.27 J/(mol·K)

Chemical properties

Oxidation states

+6

Electronegativity

2.36 (Pauling Scale)

Ionisation energy

7.98 eV
1st 770, 2nd 1,700 kJ/mol

Electron affinity

0.815 eV

Atomic radius

empirical 162, covalent 162, van der Waals 210 pm

Ionic radius

W⁴⁺ 66; W⁵⁺ 62; W⁶⁺ 60 pm

Reactivity

A group 6 refractory metal with the highest melting point of any element; in bulk it is mostly unreactive because a surface oxide protects it, but it takes every oxidation state from -2 to +6, the +6 tungstates and polytungstates dominating its aqueous chemistry.

with water

Does not react with water.

with oxygen, air

No reaction with air at room temperature; the red-hot metal oxidises to the yellow trioxide: $\ce{2 W + 3 O2 -> 2 WO3}$, so hot tungsten must be protected, and the fine powder is pyrophoric.

with acids

Attacked only slightly by most mineral acids; a mixture of hydrofluoric and nitric acid dissolves it, and fused alkali with an oxidant converts it to tungstate: $\ce{WO3 + 2 NaOH -> Na2WO4 + H2O}$, the trioxide dissolving in base.

with halogens

Fluorine attacks it at room temperature to the gaseous hexafluoride: $\ce{W + 3 F2 -> WF6}$, chlorine and bromine react at about $\ce{250 C: W + 3 Cl2 -> WCl6}$, and iodine only when hot.

Typical compounds

• WO₃ tungsten(VI) oxide
  yellow tungstic oxide, dissolves in alkali to tungstate
• WC tungsten carbide
  extremely hard, cutting tools and drill tips
• WF₆ tungsten hexafluoride
  colourless gas, deposits tungsten in chip making
• WCl₆ tungsten hexachloride
  dark blue-black volatile chloride
• WS₂ tungsten disulfide
  dry lubricant stable to 500 C
• Na₂WO₄ sodium tungstate
  soluble tungstate, feedstock for tungsten chemistry

Occurrence, production and use

Crustal abundance

1.25 milligrams per kilogram

Oceanic abundance

1×10-4 milligrams per liter

Occurrence and sources

• scheelite (CaWO4) and wolframite ((Fe,Mn)WO4)
  China (largest deposits), Vietnam, Russia, North Korea, Bolivia, Rwanda, Australia, Austria, Spain, Portugal; resources on every continent except Antarctica
• crustal and oceanic abundance
  about 1 ppm ¹; 1.25 mg/kg crust and 0.0001 mg/L seawater ²

Extraction, production

Concentrate to ammonium paratungstate and tungsten oxide

ammonium paratungstate (APT) is the traded intermediate named by USGS; the digestion chemistry is not stated

Hydrogen reduction of tungsten oxide to metal powder

$\ce{WO3 (s) + 3 H2 (g) -> W (s) + 3 H2O (g)}$

RSC states the metal is obtained by reducing tungsten oxide with hydrogen or carbon; water is the only possible product of hydrogen reduction; the carbon variant is left open because the carbon oxide product is not named

Tungsten carbide synthesis

$\ce{W (s) + C (s) -> WC (s)}$

RSC states tungsten and carbon powders are mixed and heated to 2200 C

Uses

Pure tungsten is a light gray or whitish metal that is soft enough to be cut with a hacksaw and ductile enough to be drawn into wire or extruded into various shapes. If contaminated with other materials, tungsten becomes brittle and difficult to work with. Tungsten has the highest melting point of all metallic elements and is used to make filaments for incandescent light bulbs, fluorescent light bulbs and television tubes. Tungsten expands at nearly the same rate as borosilicate glass and is used to make metal to glass seals. Tungsten is also used as a target for X-ray production, as heating elements in electric furnaces and for parts of spacecraft and missiles which must withstand high temperatures.

Tungsten is alloyed with steel to form tough metals that are stable at high temperatures. Tungsten-steel alloys are used to make such things as high speed cutting tools and rocket engine nozzles.

Tungsten carbide (WC) is an extremely hard tungsten compound. It is used in the tips of drill bits, high speed cutting tools and in mining machinery. Tungsten disulfide (WS2) is a dry lubricant that can be used to temperatures as high as 500°C. Tungsten forms compounds with calcium and magnesium that have phosphorescent properties and are used in fluorescent light bulbs.

Tungsten and its alloys are used extensively for filaments for electric lamps, electron and television tubes, and for metal evaporation work; for electrical contact points for automobile distributors; X-ray targets; windings and heating elements for electrical furnaces; and for numerous spacecraft and high-temperature applications. High-speed tool steels, Hastelloy(R), Stellite(R), and many other alloys contain tungsten. Tungsten carbide is of great importance to the metal-working, mining, and petroleum industries. Calcium and magnesium tungstates are widely used in fluorescent lighting; other salts of tungsten are used in the chemical and tanning industries. Tungsten disulfide is a dry, high-temperature lubricant, stable to 500C. Tungsten bronzes and other tungsten compounds are used in paints.

• Cemented carbide tools
  • cutting, drilling and wear-resistant parts for construction, metalworking, mining and oil and gas drilling
  • dental drills
  about 60 percent of US tungsten consumption in 2024 (usgs-mcs2025-tungsten)
• Steel and alloys: tool and specialty steels, tungsten heavy alloys, high-temperature alloys
• Electrical, lighting and welding
  • arc-welding electrodes, furnace heating elements, filaments and wires
  • calcium and magnesium tungstate phosphors in fluorescent lamps
• Chemicals
  • tungsten chemicals, tungstates and oxides
  • tungsten heavy liquids replacing thallium in mineral separation
• Mining: scheelite and wolframite mining; tungsten ore extraction is covered by the extractive-waste BREF questionnaires

Safety, toxicity

GHS classification, signal word Danger

• H228 Flammable solid Flammable solids
• H252 Self-heating in large quantities; may catch fire Self-heating substances and mixtures
• H320 Causes eye irritation Serious eye damage/eye irritation
• H335 May cause respiratory irritation Specific target organ toxicity, single exposure; Respiratory tract irritation

Discovery and name

Discovered by

Juan José Elhuyar and Fausto Elhuyar

Discovered

1783

First isolated

not in sources

Named by

Torbern Bergman

Origin of the name

the old Swedish name for the mineral scheelite, from which it was isolated; means 'heavy stone'

Pure tungsten is a steel-gray to tin-white metal. Very pure tungsten can be cut with a hacksaw, forged, spun, drawn, and extruded. The impure metal is brittle and can be worked only with difficulty. Tungsten has the highest melting point of all metals, and at temperatures over 1650°C has the highest tensile strength. The metal oxidizes in air and must be protected at elevated temperatures. It has excellent corrosion resistance and is attacked only slightly by most mineral acids. The thermal expansion is about the same as borosilicate glass, which makes the metal useful for glass-to-metal seals.