• Fluoride

Fluoride emissions result from using a cryolite solution containing approximately 50% fluoride. Large capacity ventilation systems connected to each pot capture and scrub emissions in a process that is about 99.9% efficient. Alumina is also used to capture fluorides, which are recycled when the fluorinated alumina is returned to the pots.

 

A small percentage of emissions is not captured by the scrubbers and escapes directly through the roof vents of the electrolysis buildings. In the Söderberg potrooms at Baie-Comeau, capture rate efficiency is lower than in the pre-bake pots and a higher proportion of contaminants is therefore released through the roof vents.

 


 

 

The graph combines the average total fluoride stack emissions from gas treatment centers and potroom roof vents for each smelter. An annual emissions standard of 0.95 kg F/mt Al took effect in 2011. This requirement has been applied to the Deschambault Smelter since 2007.
 

In 2015, fluoride emissions from vents at the Baie-Comeau Smelter increased slightly, notably due to repair work on its scrubbers, sometimes requiring shutdowns.

 

At the Bécancour Smelter, fluoride emissions were slightly lower in 2015 due to sustained efforts to improve process stability. Emissions at the Deschambault Smelter, which is equipped with double-capture technology, are lower than at the other plants. Improvements in the control of carbon dust generation also contributed to reducing emissions in 2015.