The Control of Fluoride Concentration in ETİ Alüminyum Bayer Refinery Liquor

Abstract

In the ETI Alüminyum Bayer Process liquors, fluoride is evident as an undesirable impurity, because it presents itself as a precipitate of Sodium Fluoride (NaF) in the higher concentration liquors, which has two mal effects, one of which limits the caustic concentration that ETI can attain, and the other is its solid phase presents as scale.

Spent liquor from precipitation is fed to evaporators. To improve alumina extraction in autoclave liquor it was decided that the strong liquor caustic concentration be gradually increased. It was noticed that scale formation in the strong liquor pumps and pipelines dramatically increased. XRF and XRD characterized the scale as ‘Villiaumite’ (NaF). Research on Villiaumite found that it started to precipitate at higher caustic concentrations. The solubility of NaF was evaluated and saturation levels were determined. As a result of this study control of NaF precipitation is practiced by ETI.