Because of their potential occupational safety and health implications, the formation of volatile substances is of interest to many hydrometallurgical plants, including alumina refineries using the Bayer process. Rigorous thermodynamic models for various groups of volatile compounds have been incorporated into the database of the Murdoch Bayer liquor model to simulate their distribution among different process streams. Under conditions prevailing in a high-temperature digestion stage of the Bayer process, only hydrogen, low hydrocarbons, and mercury are predicted to be present in the gas phase in significant amounts. The other volatiles primarily remain dissolved in the liquor and are therefore transported to the flash vessels. Flash train simulations confirm that hydrophobic substances accumulate in the vapor phase where they can be destroyed by thermal oxidation. However, large fractions of hydrophilic substances are predicted to dissolve in the aqueous phases. They may therefore be released into the environment when digestion condensate is used for washing and dilution purposes. Mercury constitutes a special case because liquid Hg may precipitate in the first heat exchanger when the condensate/vapor ratio is high.