SUPERNATANT LIQUOR NEUTRALISATION WITH SEAWATER AND BAYER TAILINGS MUD VIA DEEP CONE THICKENER

The purpose of seawater neutralisation of supernatant pond liquor (SNL) is to precipitate heavy metal impurities to such an extent that the neutralised SNL may be discharged out to sea, thus reducing the total tailings dam inventory. Alcan Gove is actively pursuing several avenues of enhancing this process to increase the rate of processing SNL and quality of effluent for disposal.

CSIRO conducted bench tests that looked at the addition of red mud slurry to the seawater, SNL mix, and concluded that the final vanadium concentration could be significantly reduced. This led to a pilot study conducted in 2000 which confirmed that the addition of red mud during the neutralisation process enhanced the precipitation of vanadium from SNL. Unfortunately, separation of precipitated material remained problematic and was considered to have resulted from design irregularities in the equipment used for the trial.

A large-scale plant trial using a Deep Cone Thickener was commissioned in early 2002 to validate the original findings and to improve separation of precipitated material from the effluent. The findings will be used to develop a continuous full-scale facility for the treatment of SNL.

Further laboratory studies have indicated that addition of alkaline earth chemicals such as calcium and magnesium hydroxides may further enhance the neutralisation process. A long-term investigation is now underway to study their efficiency, where to best introduce them into the waste disposal system and whether they would have any detrimental effect on a mud based neutralisation system.

This paper describes the progress achieved to date in all these fields of research.