Description of tungsten trioxide

Tungsten trioxide, also known as tungsten(VI) oxide or tungstic anhydride, WO₃, is a chemical compound containing oxygen and the transition metal tungsten. It is obtained as an intermediate in the recovery of tungsten from its minerals.

Tungsten ores are treated with alkalis to produce WO₃. Further reaction with carbon or hydrogen gas reduces tungsten trioxide to the pure metal.

2 WO₃ + 3 C + heat → 2 W + 3 CO₂

WO₃ + 3 H₂ + heat → W + 3 H₂O

Tungsten(VI) oxide occurs naturally in form of hydrates, which include minerals: tungstite WO₃·H₂O, meymacite WO₃·2H₂O and hydrotungstite (of same composition as meymacite, however sometimes written as H₂WO₄). These minerals are rare to very rare secondary tungsten minerals.