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How does roasting cinnabar in air release elemental mercury?
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mercury processing
Mercury in the bulb of a thermometer.
Roasting cinnabar (mercury sulfide) in air is a pyrometallurgical process that effectively liberates elemental mercury through a chemical reaction driven by heat.12
When the ore is heated in the presence of air, the oxygen in the air reacts with the sulfur in the cinnabar to form sulfur dioxide. This oxidation-reduction reaction decomposes the sulfide ore, releasing the metal at temperatures exceeding its boiling point of 356.62 °C (673.91 °F). Because the mercury is liberated as a vapour, it can be separated from the solid residue and subsequently collected by passing the gases through a series of cooling tubes, where the mercury vapour condenses into its liquid phase.12