Titanium

Typical wastewaters

• municipal sewage particulate TiO₂ (pigment and nanoparticle) from sunscreens, paints, coatings and foods, 100 to nearly 3,000 µg/L in raw sewage, mostly in particles larger than 0.7 µm Westerhoff and others 2011: treated effluent below 25 µg/L at ten plants, with 4 to 30 nm titanium oxide spheres seen by electron microscopy

1 · Identity

Symbol, number

Ti, 22

Oxidation states in water

+4 only in practice, as TiO₂ (rutile, anatase, amorphous) and hydrous titanium oxide colloids; dissolved Ti(OH)₄ and its hydroxo complexes exist only at trace levels. +3 is a reducing laboratory state with no water occurrence. 0 as the metal, passivated by its own oxide.

Note

The element entry covers the ninth most abundant element, ilmenite and rutile, TiCl₄ and the pigment industry. In water titanium is a particle.

2 · Occurrence in water

Natural sources

Ilmenite, rutile and sphene grains and TiO₂ bearing clays in suspended sediment; dissolved titanium in natural water is at trace levels because of the insolubility of TiO₂ (element entry).

Anthropogenic sources

Titanium dioxide pigment and nanoparticle products (sunscreens, paints, coatings, foods) washed into sewers; titanium dioxide pigment plant effluent (sulfate and chloride process wastes in the ledger's chemical chapter); TiO₂ photocatalyst slurries in research and pilot plants; titanium metal releases nothing measurable.

3 · Speciation

Ti(IV) hydrolyses completely; whatever titanium enters water ends as TiO₂ or hydrous titanium oxide particles, from single nanoparticles and 50 to a few hundred nanometre aggregates to pigment grains. Dissolved titanium is negligible and has no speciation story worth a table. The treatment relevant property is the particle: it is removed with solids and it photocatalyses under near ultraviolet light.

Solubility

TiO₂ is insoluble and chemically inert (element entry); no dissolved titanium concentration was read.

Hydrolysis

Complete at any natural pH.

Complexation

Fluoride and peroxide complexes exist in the laboratory; none matter in water treatment.

Precipitates

TiO₂ (anatase, rutile, amorphous) and hydrous titanium oxide.

4 · Role in treatment

5 · Removal and control

6 · Analytics

Sampling pitfalls

Dissolved titanium is meaningless; report size fractions. Incomplete digestion of TiO₂ underestimates total titanium.

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

Not addressed in the sources read for ingestion via water; the element entry describes TiO₂ as inert.

Bioaccumulation

Not addressed in the sources read.

Ecotoxicity

The wastewater studies were motivated by the possible ecological risk of nanoparticles in effluent; no criterion or figure was read.

Flags

• Kiser and others 2009 and Westerhoff and others 2011 were read as abstracts.
• The photocatalysis mechanism is from a 2022 review read as a summary; no full scale water treatment plant using TiO₂ photocatalysis was found in it.
• The desalination and chlor-alkali material uses are cross referenced to the element entry, not to a water source read.

Gaps

• No natural water dissolved titanium concentration was read.
• No toxicity or ecotoxicity figure for TiO₂ nanoparticles in water was read.
• Titanium dioxide pigment plant effluent figures belong to the ledger's chemical chapter and were not read here.
• No analytical detection limit for titanium was read.

Sources

Identity

Name and symbol

Titanium, Ti

Atomic number

22 protons

Position

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

CAS number

7440-32-6

Atomic structure

Atomic mass

47.867 u

Electron configuration

1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d²
[Ar] 4s²³d²

Electrons per shell

2, 8, 10, 2

Valence electrons

4 ns and (n-1)d

Physical properties

State at room temperature

Solid

Melting point

1,941 K (1,667.85 °C)

Boiling point

3,560 K (3,286.85 °C)

Density

4.5 g/cm3

Appearance

silvery grey-white metallic

Thermal conductivity

21.9 W/(m·K)

Electrical resistivity

420 nΩ·m at 20 °C

Electrical conductivity

2.38 MS/m

Crystal structure

hexagonal close packed

Molar heat capacity

25.06 J/(mol·K)

Chemical properties

Oxidation states

+4, +3, +2

Electronegativity

1.54 (Pauling Scale)

Ionisation energy

6.828 eV
1st 658.8, 2nd 1,309.8, 3rd 2,652.5 kJ/mol

Electron affinity

0.079 eV

Atomic radius

empirical 160, covalent 160, van der Waals 187 pm

Ionic radius

Ti²⁺ 86; Ti³⁺ 67; Ti⁴⁺ 61 pm

Reactivity

A group 4 transition metal ([Ar] 3d2 4s2) dominated by the +4 state; a tenacious oxide film makes the bulk metal exceptionally corrosion resistant to sea water, chloride solutions, aqua regia and chlorine gas, yet it burns in air and is one of the few elements that burn in pure nitrogen.

with water

Does not react with water; the metal has excellent resistance to sea water and is used for ship parts and desalination plant.

with oxygen, air

Protected by its oxide film at room temperature; combines with oxygen at red heat, readily at 1200 C in air and 610 C in pure oxygen, burning to titanium dioxide, and at 800 C it also burns in nitrogen to the nitride: $\ce{Ti + O2 -> TiO2}$

with acids

Resists dilute sulfuric and hydrochloric acid, most organic acids and oxidising acids, but dissolves in dilute hydrofluoric acid, hot hydrochloric acid, hot sulfuric acid and other concentrated acids.

with halogens

Fairly inert to the halogens at room temperature, but combines violently with chlorine and bromine at 550 C to the tetrahalides: $\ce{Ti + 2 Cl2 -> TiCl4}$

Typical compounds

• TiO₂ titanium dioxide rutile, anatase; the white pigment and photocatalyst
• TiCl₄ titanium tetrachloride fumes in moist air; Kroll feed, smoke screens
• TiCl₃ titanium trichloride Ziegler-Natta polyolefin catalyst
• TiN titanium nitride refractory, extremely hard coating
• TiC titanium carbide cutting tools and coatings
• FeTiO₃ ilmenite the main ore with rutile

Occurrence, production and use

Crustal abundance

5.65×103 milligrams per kilogram

Oceanic abundance

1×10-3 milligrams per liter

Occurrence and sources

Titanium is present in meteorites and the sun. Rocks obtained during the Apollo 17 lunar mission showed presence of 12.1% TiO2; rocks obtained during earlier Apollo missions show lower percentages.

Titanium oxide bands are prominent in the spectra of M-type stars. The element is the ninth most abundant in the crust of the earth. Titanium is almost always present in igneous rocks and in the sediments derived from them.

It occurs in the minerals rutile, ilmenite, and sphene, and is present in titanates and in many iron ores. Titanium is present in ash of coal, in plants, and in human body.

The metal was a laboratory curiosity until Kroll, in 1946, showed that titanium could be produced commercially by reducing titanium tetrachloride with magnesium. This method is still largely used for producing the metal. The metal can be purified by decomposing the iodide.

• ilmenite (FeTiO3) beach and inland heavy mineral sands and hard rock deposits; about 90 percent of world titanium mineral consumption; mined in China, Mozambique, South Africa, Australia, Canada, Norway, Senegal, Madagascar and India; reserves over 510 million tonnes of TiO2
• rutile (TiO2) heavy mineral sands in Australia, South Africa, Sierra Leone, Kenya and Ukraine; reserves over 46 million tonnes of TiO2
• titaniferous magnetite and sphene (CaTiSiO5) igneous rocks and many iron ores; titaniferous magnetite is smelted to titanium slag in Canada, South Africa and Norway

Extraction, production

Titanium dioxide pigment by the sulphate or chloride process

$\ce{TiCl4 (g) + O2 (g) -> TiO2 (s) + 2 Cl2 (g)}$

Both routes start from ilmenite or its upgraded forms (titanium slag, synthetic rutile, rutile) and end as TiO2 pigment; the sulphate process digests the ore in sulphuric acid and the chloride process chlorinates it to TiCl4 and burns that to TiO2. The equation given is the chloride process oxidation step, taken from the added secondary source. United States pigment production 850,000 tonnes in 2024 (estimate); world capacity 9.8 million tonnes, of which China 5.5 million.

Kroll process: magnesium reduction of titanium tetrachloride to sponge metal

$\ce{TiCl4 + 2 Mg -> Ti + 2 MgCl2}$

Balanced from the reactants and products stated by the sources (titanium tetrachloride reduced with magnesium, the process Kroll showed in 1946 and still the commercial route). World sponge production about 320,000 tonnes in 2024 excluding the United States: China 220,000, Japan 55,000, Russia 20,000, Saudi Arabia 15,000, Kazakhstan 14,000. The United States imported about 40,000 tonnes of sponge in 2024.

Uses

Titanium is a strong, light metal. It is as strong as steel and twice as strong as aluminum, but is 45% lighter than steel and only 60% heavier than aluminum. Titanium is not easily corroded by sea water and is used in propeller shafts, rigging and other parts of boats that are exposed to sea water. Titanium and titanium alloys are used in airplanes, missiles and rockets where strength, low weight and resistance to high temperatures are important. Since titanium does not react within the human body, it is used to create artificial hips, pins for setting bones and for other biological implants. Unfortunately, the high cost of titanium has limited its widespread use.

Titanium oxide (TiO2) is used as a pigment to create white paint and accounts for the largest use of the element. Pure titanium oxide is relatively clear and is used to create titania, an artificial gemstone. Titanium tetrachloride (TiCl4), another titanium compound, has been used to make smoke screens.

A final bit of titanium trivia titanium is one of the few elements that will burn in an atmosphere of pure nitrogen.

Titanium is important as an alloying agent with aluminum, molybdenum, manganese, iron, and other metals. Alloys of titanium are principally used for aircraft and missiles where lightweight strength and ability to withstand extremes of temperature are important.

Titanium is as strong as steel, but 45% lighter. It is 60% heavier than aluminum, but twice as strong.

Titanium has potential use in desalination plants for converting sea water into fresh water. The metal has excellent resistance to sea water and is used for propeller shafts, rigging, and other parts of ships exposed to salt water. A titanium anode coated with platinum has been used to provide cathodic protection from corrosion by salt water.

It is produced artificially for use as a gemstone, but it is relatively soft. Star sapphires and rubies exhibit their asterism as a result of the presence of TiO2.

Titanium dioxide is extensively used for both house paint and artist's paint, because it is permanent and has good covering power. Titanium oxide pigment accounts for the largest use of the element. Titanium paint is an excellent reflector of infrared, and is extensively used in solar observatories where heat causes poor viewing conditions.

Titanium tetrachloride is used to iridize glass. This compound fumes strongly in air and has been used to produce smoke screens.

• Pigments and coatings: TiO2 pigment in paints, lacquers and varnishes, plastics and paper (in descending order); catalysts, ceramics, coated fabrics and textiles, floor coverings, printing ink, roofing granules; sunscreens more than 95 percent of titanium mineral concentrates were consumed by pigment producers in 2024 (USGS, US figure)
• Chemicals: coated titanium anodes in membrane and diaphragm chlor-alkali cells, listed by the ledger's chemical chapter among the cell materials; titanium process equipment for chlorine and chloride service, which the metal resists
• Aerospace and engineering alloys: airframes, engines, missiles and spacecraft, the majority of titanium metal use; armour, marine hardware, power plant condensers, desalination plant, medical implants and dental implants
• Polymers: titanium based Ziegler catalysts for high density polyethylene, alongside chromium based Phillips catalysts; titanium dioxide added to unsaturated polyester resins for pigmented grades
• Textiles: nano dispersions of titanium dioxide padded onto fabrics as anti UV finishes (Textiles BREF); TiO2 as a delustrant and white pigment in coated fabrics and textiles
• Food and beverage: titanium dioxide as the white colour additive E171, listed in the food chapter's additive register

Safety, toxicity

GHS classification, signal word Danger

• H228 Flammable solid Flammable solids
• H250 Catches fire spontaneously if exposed to air Pyrophoric liquids
• H251 Self-heating; may catch fire Self-heating substances and mixtures

Discovery and name

Discovered by

William Gregor

Discovered

1791

First isolated

Jöns Jakob Berzelius

Named by

Martin Heinrich Klaproth

Origin of the name

after the Titans of Greek mythology

Titanium, when pure, is a lustrous, white metal. It has a low density, good strength, is easily fabricated, and has excellent corrosion resistance. It is ductile only when it is free of oxygen. The metal, which burns in air, is the only element that burns in nitrogen.

Titanium is resistant to dilute sulfuric and hydrochloric acid, most organic acids, most chlorine gas, and chloride solutions.

Natural titanium is reported to become very radioactive after bombardment with deuterons. The emitted radiations are mostly positrons and hard gamma rays. The metal is dimorphic. The hexagonal alpha form changes to the cubic beta form very slowly at about 880°C. The metal combines with oxygen at red heat, and with chlorine at 550°C.

Titanium metal is considered to be physiologically inert. When pure, titanium dioxide is relatively clear and has an extremely high index of refraction with an optical dispersion higher than diamond.