Fluoride emissions refer to the release of fluoride-containing compounds — primarily hydrogen fluoride (HF) and particulate fluorides — into the atmosphere or surrounding environment during high-temperature industrial processes. In the mining industry, fluoride emissions are of particular concern in alumina and aluminum smelting operations that process bauxite ore, as well as in certain gold and iron ore roasting and sintering processes where fluoride-bearing gangue minerals are present.
In the aluminum smelting industry, which is the downstream product of bauxite mining and alumina refining, electrolytic reduction cells (Hall-Héroult cells) use cryolite (Na₃AlF₆) and aluminum fluoride (AlF₃) as electrolyte components. At operating temperatures of approximately 960°C, fluoride gases and fine particulate fluorides are emitted from these pots. These emissions can cause severe health effects in workers, including skeletal fluorosis (caused by bone fluoride accumulation), dental fluorosis, and respiratory irritation. Communities and livestock near smelters are also vulnerable if emissions are not adequately controlled.
In iron ore sintering, fluorite (CaF₂) is occasionally used as a flux, generating fluoride-bearing off-gases during sintering. Regulatory bodies in most countries set stringent maximum permissible concentrations (MPCs) for fluoride in ambient air and workplace environments. Engineering controls include dry scrubbing with alumina in aluminum smelters — which simultaneously captures fluoride and recovers it as a valuable raw material — and wet scrubbing systems in other applications.
Mining companies are required to conduct regular ambient fluoride monitoring programs around their processing facilities, including fluoride-in-vegetation and fluoride-in-air measurements. Fluoride emission inventories form a core component of environmental impact assessments (EIAs) and annual environmental compliance reports for mining operations worldwide.