Thallium

A highly toxic by-product of zinc, lead and copper smelting, used in gamma detectors, infrared optics and some heart scans.

Tech & minor metals · No. 53

• Not on a critical list

Thallium is so toxic US drinking water may hold just 2 parts per billion, yet heart scans and gamma detectors use it.

Chart: Illustration: Thallium

Where it comes from

Chart: Map of where it comes from

Commercial thallium comes from traces in copper, lead and zinc sulphide ores. Roasting sends it into the flue dust, which is leached and refined to 99.99% granules.

Three things to know

1. Thallium averages about 0.7 parts per million in the crust, but most is locked in potassium minerals where it cannot be recovered.
2. The US has produced no thallium since 1981, and the price has stayed within $8,400-9,500/kg since 2021.
3. Technetium-99m has displaced thallium-201 in cardiac imaging, so medical demand is slowly shrinking.

The journey

1. 1 Sulphide oresZinc, lead and copper ores
2. 2 SmeltingRoasted and smelted for base metals
3. 3 Flue dustThallium collects in roaster dust
4. 4 LeachingThallium recovered from the dust
5. 5 Refining99.99% granules and compounds

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