OPTIMISING BAUXITE RESIDUE DELIQUORING AND CONSOLIDATION

The eff ective management of bauxite residue represents one of the most signifi cant long-term issues facing the alumina industry. Although signifi cant progress has been made in recent years in pre-disposal thickening technology, understanding of the principles underlying post-disposal management of residue to enhance deliquoring (Mud Farming) using twin Archimedes Screw Tractors (ASTs commonly known as Amphirols) is not as advanced. Reviews of several operations have indicated examples of site-specifi c methodologies with limited relevance to the underlying dynamics and reference to, or reliance on common rules of thumb that lead to inconsistent performance across residue storage areas or between operations (using the same equipment and similar residue characteristics) through ineff ective application of ASTs for homogenous, full-depth residue consolidation. Data is presented of an optimised consolidation management approach developed at BWAPL to ensure residue consolidation to desired strength targets with existing equipment whilst minimising disposal area footprint. The regime requires strict control around residue deposition practice with key parameters being residue depth, consolidation time and number of active cells determining open area and number of ASTs. Other important aspects to be considered include seasonal conditions such as rain extent and dust formation risk and control. A simple model can be applied to defi ne active working area requirements based on residue characteristics, production rates and required AST coverage capacity. This approach allows BWAPL to operate at higher residue deposition intensities and to consolidate residue faster and to higher strengths independent of residue solids content. Although proven for the BWAPL case, the logic is transferrable to any alumina residue or similar slurry deposition operation.