Thallium - Tl

Thallium — chemical properties and water context

Thallium is a soft, silvery metal. Thallium and its compounds are highly toxic; the element is relevant to water engineers when it occurs in groundwater or in emissions, mining and metal-refining streams.

Atomic number	81
Standard atomic weight	[204.382, 204.385] g/mol
Density	11.8 g/cm3
Melting point	304 °C
Boiling point	1473 °C
Electron configuration	[Xe] 4f14 5d10 6s2 6p1

Chemical properties

Thallium is in Group 13 and Period 6. It commonly occurs in the +1 oxidation state in water, although +3 compounds also exist. Thallium compounds can be soluble, and its speciation and mobility depend on redox conditions, pH and the surrounding mineral chemistry.

Uses and applications

Thallium has limited uses because of its toxicity. It has been used in electronics, photoelectric cells and specialty glass. It may enter water through leaching of mineral deposits or through ore processing and other industrial activity.

Thallium in water treatment

The U.S. EPA identifies adsorptive media as a treatment option for thallium. Media selection and performance depend on the specific sorbent, pH and thallium valence; a real-water test is important before design. Monitor the relevant dissolved or total fraction and manage spent media or regenerant containing concentrated thallium.

Environmental and health context

Thallium has no known biological role and can be harmful at elevated exposure. Because thallium may occur as different ionic forms, interpret analytical results with attention to speciation and source. Apply the drinking-water limits and monitoring requirements for the relevant jurisdiction.

Back to the periodic table of elements