Bauxite contains trace amounts of mercury (0.02–1.5 mg/kg) but due to the large mass of bauxite processed in Bayer refining, mercury can accumulate in Bayer liquor, aluminium hydrate, and oxalate. The mercury emissions to air from Bayer refineries were speciated for elemental, ionic, and particulate mercury using a FMSS (flue gas mercury sorbent speciation) method. The mercury emissions to air from Bayer refineries are almost 100% elemental mercury from studies of emissions from Alcoa Bayer refineries. These emissions pose very little environmental risk to the local or regional environment because the residence time of elemental mercury in the atmosphere is 1–1.5 years. Elemental mercury emissions do contribute to the global atmospheric reservoir of mercury and reducing mercury emissions is important in reducing anthropogenic contributions to the global atmospheric mercury budget.
The study showed that mercury losses from Bayer refineries differed significantly from refinery to refinery. Some refineries had significant mercury emissions from calcination due to mercury in the aluminium hydrate while other refineries had a significantly higher portion of the mercury emissions from digestion vent gases. The data showed losses of mercury to air (emissions) from digestion vent gases for all the refineries studied. High concentrations of mercury on oxalate cake were found for some refineries. The proportion of input mercury reporting to the residue ranged from 12–60% for all Alcoa refineries.