Zirconium

Typical wastewaters

• water treatment residuals where zirconium coagulants or adsorbents are used hydrous zirconia in the floc and in spent fluoride and phosphate adsorbents; dissolved zirconium negligible
• zircon milling, zirconia ceramic works and nuclear fuel cladding manufacture particulate zircon and hydrous zirconia; Zr(IV) is fully hydrolysed and insoluble at any natural pH named by the element entry; no effluent figure read

1 · Identity

Symbol, number

Zr, 40

Oxidation states in water

+4 only; hydrolysed to Zr(OH)₄^0 and Zr(OH)₅⁻ (the seawater species) and polymerised to hydrous zirconia

Note

The element entry covers the corrosion resistant metal, zircon and ZrO₂. In water zirconium is a hard, fully hydrolysed tetravalent cation whose hydroxide surface binds fluoride and oxyanions.

2 · Occurrence in water

Natural sources

Weathering of zircon, which is nearly insoluble, so dissolved zirconium is at picomolar to nanomolar levels; Japanese lake and spring waters 0.29 to 2.8 µg/L; seawater about 160 pmol/kg, depleted at the surface and enriched with depth, residence time 5600 years.

Anthropogenic sources

Zircon milling and zirconia ceramic works, nuclear fuel cladding manufacture (element entry); coagulant and adsorbent residuals where zirconium reagents are used. Zirconium-95 is a fission product.

3 · Speciation

Fully hydrolysed Zr(IV): neutral Zr(OH)₄ and the anion Zr(OH)₅⁻ in seawater; at higher concentration the hydroxo species polymerise to hydrous zirconia, which is the working surface of every zirconium coagulant and adsorbent. Fluoride complexes zirconium strongly (the element entry notes that fluoride is what dissolves the metal), which is the chemistry behind defluoridation.

Solubility

Very low; controlled by hydrous zirconia and zircon.

Hydrolysis

Complete at natural pH; polymerisation above micromolar concentration.

Complexation

Fluoride strongly; phosphate on surfaces; carbonate not read.

Precipitates

Hydrous ZrO₂, Zr(OH)₄, zirconium phosphate.

4 · Role in treatment

5 · Removal and control

6 · Analytics

Sampling pitfalls

Zirconium sorbs to container walls and colloids; acidify with fluoride-free acid only if the method tolerates it, and expect most of the total to be particulate. Fluoride in the sample keeps it dissolved and shifts speciation.

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; the dye coagulation study found no toxicity of zirconium oxychloride up to 500 mg/L in its assay.

Bioaccumulation

Not read.

Ecotoxicity

Not read.

Flags

• The coagulant performance figures are single laboratory studies on one water each; the NOM comparison is against aluminium sulfate only.
• Adsorbent capacities are Langmuir maxima from batch tests on synthetic solutions except where a real wastewater is named.
• The seawater speciation and residence time come from a periodic table web page without named author.
• Whether the 57.98 and 49.02 percent NOM and phenol figures are absolute removals or the margin over aluminium sulfate is ambiguous in the abstract; the wording is kept as given.

Gaps

• No river or groundwater survey beyond the 1978 Japanese springs was read; world river zirconium was not reachable.
• No hydrolysis constants or solubility product were read.
• The zirconium fluoride adsorbent review (hydrous zirconium oxide up to 68 mg/g at pH 7 in a search summary) was not reachable, so that figure is not written.
• No full scale coagulant dose or alkalinity consumption for zirconium oxychloride was read.
• No ecotoxicity data were read.
• No GCC discharge standard was read.

Sources

Identity

Name and symbol

Zirconium, Zr

Atomic number

40 protons

Position

group 4 · period 5 · d-block · transition metal

CAS number

7440-67-7

Atomic structure

Atomic mass

91.222 u

Electron configuration

1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s² 4d²
[Kr] 5s²⁴d²

Electrons per shell

2, 8, 18, 10, 2

Valence electrons

4 ns and (n-1)d

Physical properties

State at room temperature

Solid

Melting point

2,128 K (1,854.85 °C)

Boiling point

4,682 K (4,408.85 °C)

Density

6.52 g/cm3

Appearance

silvery white

Thermal conductivity

22.6 W/(m·K)

Electrical resistivity

421 nΩ·m at 20 °C

Electrical conductivity

2.38 MS/m

Crystal structure

hexagonal close-packed

Molar heat capacity

25.36 J/(mol·K)

Chemical properties

Oxidation states

+4

Electronegativity

1.33 (Pauling Scale)

Ionisation energy

6.634 eV
1st 640.1, 2nd 1,270, 3rd 2,218 kJ/mol

Electron affinity

0.426 eV

Atomic radius

empirical 175, covalent 175, van der Waals 186 pm

Ionic radius

Zr⁴⁺ 72 pm

Reactivity

A group 4 transition metal that is thermodynamically very reactive but in practice highly corrosion resistant, because a tight oxide film protects it from acids, alkalis and sea water; powdered zirconium is highly flammable.

with water

Does not react with water at ordinary temperatures; the reaction is very slow below 100 C but rapid above 900 C, where steam oxidises it with release of hydrogen: $\ce{Zr + 2 H2O -> ZrO2 + 2 H2}$.

with oxygen, air

Protected in air by a thin oxide film; the powder is highly flammable and burns to the dioxide: $\ce{Zr + O2 -> ZrO2}$.

with acids

Exceptionally resistant to most acids and alkalis, including aqua regia; it dissolves in hydrochloric or sulfuric acid when fluoride is present, and hydrofluoric acid attacks it.

with halogens

Combines with the halogens on heating to the volatile tetrahalides: $\ce{Zr + 2 Cl2 -> ZrCl4}$.

Typical compounds

• ZrO₂ zirconium dioxide zirconia; refractory crucibles, ceramic knives, cubic zirconia gems
• ZrSiO₄ zircon the ore; foundry sand, glaze opacifier, gemstone
• ZrCl₄ zirconium tetrachloride intermediate in the Kroll process for the metal
• ZrF₄ zirconium tetrafluoride component of fluoride glasses
• ZrH₂ zirconium hydride formed on absorbing hydrogen; neutron moderator

Occurrence, production and use

Crustal abundance

1.65×102 milligrams per kilogram

Oceanic abundance

3×10-5 milligrams per liter

Occurrence and sources

Zirconium is produced from the mineral zircon (ZrSiO4). It is found in abundance in S-type stars, and has been identified in the sun and meteorites. Analysis of lunar rock samples obtained during the various Apollo missions to the moon show a surprisingly high zirconium oxide content, compared with terrestrial rocks.

• zircon (ZrSiO4, about 65 percent ZrO2, Zr:Hf about 50:1) heavy-mineral sands mined with ilmenite, rutile and monazite in Australia, South Africa, Mozambique, Senegal, Florida and Georgia
• baddeleyite (ZrO2) mostly mined in Brazil
• crustal and oceanic abundance about 132 ppm (BGS figure via RSC); 165 mg/kg crust and 0.00003 mg/L seawater (PubChem)

Extraction, production

Zircon concentrate from heavy-mineral sands

Zircon is separated as a coproduct of titanium-mineral mining; world concentrate output about 1.5 million t in 2024; ceramics, foundry sand, opacifiers and refractories take most of it directly

Kroll-type reduction of zirconium tetrachloride with magnesium (metal)

$\ce{ZrCl4 (g) + 2 Mg (l) -> Zr (s) + 2 MgCl2 (l)}$

RSC states zircon is converted to zirconium chloride and the chloride reduced with magnesium; magnesium chloride as the co-product is implied by the reduction, not named; the zircon-to-chloride step reagents are not stated

Iodide (van Arkel and de Boer) refining to high-purity metal

$\ce{ZrI4 (g) -> Zr (s) + 2 I2 (g)}$

thermal decomposition of the tetraiodide on a hot filament, the 1925 route to pure metal

Uses

Zirconium is a corrosion resistant metal that is used in high performance pumps and valves. Since it also does not easily absorb neutrons, zirconium is widely used in nuclear reactors. The nuclear power industry uses nearly 90% of the zirconium produced each year, which must be nearly free of hafnium. Zirconium is also used as an alloying agent in steel, to make some types of surgical equipment and as a getter, a material that combines with and removes trace gases from vacuum tubes.

Zircon (ZrSiO4) is a zirconium compound that can take many different forms, the most popular of which is a clear, transparent gemstone that can be cut to look like diamond and is frequently used in jewelry. Zirconium dioxide (ZrO2) can withstand very high temperatures and is used to make crucibles and to line the walls of high temperature furnaces. Zirconium carbonate (3ZrO2·CO2·H2O) is used in lotions to treat poison ivy.

It is used extensively by the chemical industry where corrosive agents are employed. Zirconium is used as a getter in vacuum tubes, as an alloying agent in steel, in surgical appliances, photoflash bulbs, explosive primers, rayon spinnerets, lamp filaments, etc. It is used in poison ivy lotions in the form of the carbonate as it combines with urushiol. With niobium, zirconium is superconductive at low temperatures and is used to make superconductive magnets, which offer hope of direct large-scale generation of electric power. Zirconium oxide (zircon) has a high index of refraction and is used as a gem material. The impure oxide, zirconia, is used for laboratory crucibles that will withstand heat shock, for linings of metallurgical furnaces, and by the glass and ceramic industries as a refractory material. Its use as a refractory material accounts for a large share of all zirconium consumed.

• Ceramics, refractories and foundries: zircon foundry sand and mould cores; zirconia refractories, furnace linings, crucibles; opacifiers and blue and yellow zircon glaze pigments (with vanadium or praseodymium); abrasives, welding-rod coatings ceramics, foundry sand, opacifiers and refractories are the leading end uses of zircon (usgs-mcs2025-zirconium-hafnium)
• Nuclear: hafnium-free zirconium alloy fuel cladding and reactor tubing (over 100,000 m per reactor); niobium-zirconium superconducting magnets RSC states more than 90 percent of zirconium metal goes to nuclear use; USGS names nuclear energy and chemical process industries as the leading metal consumers
• Chemicals (process equipment and zirconium chemicals): corrosion-resistant vessels, piping and heat exchangers for acids and alkalis; zirconium chemicals produced by at least 11 US companies
• Mining (heavy-mineral sands): zircon recovered as a coproduct of ilmenite and rutile mining from mineral sands and from reprocessed sand tailings
• Consumer and medical products: zirconia knives and dental ceramics; cosmetics, antiperspirants, food packaging; cubic zirconia gemstones

Safety, toxicity

GHS classification, signal word Danger

• H250 Catches fire spontaneously if exposed to air Pyrophoric liquids
• H260 In contact with water releases flammable gases which may ignite spontaneously Substances and mixtures which in contact with water, emit flammable gases
• H251 Self-heating; may catch fire Self-heating substances and mixtures
• H228 Flammable solid Flammable solids
• H335 May cause respiratory irritation Specific target organ toxicity, single exposure; Respiratory tract irritation
• H317 May cause an allergic skin reaction Sensitization, Skin

Discovery and name

Discovered by

Martin Heinrich Klaproth

Discovered

1789

First isolated

Jöns Jakob Berzelius

Named by

not in sources

Origin of the name

after zircon, zargun زرگون meaning "gold-colored"

Reactor-grade zirconium is essentially free of hafnium. Zircaloy(R) is an important alloy developed specifically for nuclear applications. Zirconium is exceptionally resistant to corrosion by many common acids and alkalis, by sea water, and by other agents. Alloyed with zinc, zirconium becomes magnetic at temperatures below 35°K.