FUNDAMENTAL STUDY OF PHOTOCHEMICALLY INITIATED ORGANIC REACTIONS IN RED MUD RESIDUE DISPOSAL WASH WATER
Carter, C.M. Nunes, M.D. Baker, M.V. Ghisalberti, E.L.
At Alcoa of Australia red mud is disposed of at residue lakes, and the entrained process liquor is diluted as part of the washing process. The diluted liquor is held in lakes that are exposed to solar radiation for some months before the liquor is returned to the Bayer circuit through the red mud and sand washers. It is known that this liquor has a different organic composition to the process liquor. Since it is likely that photochemistry is at least partly responsible for this difference, the role of photochemically initiated reactions on model Bayer liquor organics has been studied.
5-Hydroxyisophthalic acid and other hydroxy aromatic carboxylic acids which model some Bayer liquor organics were each irradiated in a solution of sodium hydroxide with a UV source and the degradation was monitored by UV-Visible spectroscopy. Over twenty of the degradation products of 5-hydroxyisophthalic acid were identified using GC-MS. The effect of the sparge gas on the formation of the degradation products oxalate, malonate and succinate, and the total organic carbon concentration was investigated. The effect of the hydroxyl and carboxylic acid functionalities on the reactivity of these aromatic acids was also determined.
On the basis of this work and work by other authors a mechanism has been proposed for the degradation of 5-hydroxyisophthalic acid in alkaline solution by solar radiation. This mechanism can be applied to the other hydroxy aromatic carboxylic acids investigated in this work.