EFFECT ON ALUMINIUM SOLUBILITY WHEN ACID IS USED TO NEUTRALISE RESIDUE

The RTA Yarwun alumina refinery currently produces 1.3Mtpa of residue. Seawater is used to neutralise the residue prior to mud stacking and effluent discharge. Equipment limitations and altered process conditions have resulted in insufficient seawater being available for complete neutralisation. As a result, sulphuric acid is being used to supplement the neutralisation process. This has significantly altered the neutralisation chemistry, particularly the solubility of aluminium. It was also found that the pH required to precipitate dissolved aluminium from the supernatant liquor is significantly lower when acid is used compared to seawater.