The challenge
Poor water recovery and performance issues
AngloGold Ashanti's Sunrise Dam gold mine lies on the eastern shore of Lake Carey in the northern goldfields of Western Australia.
The mine comprises a large open pit, which began operations in 1995 and an underground mine which began production in 2003.
Ore is treated in a conventional gravity and carbon-in-leach processing plant. The tailings waste generated from the processing plant are thickened in a 24 m diameter thickener unit and pumped to a tailings storage facility.
Problems with low yield stress and low underflow solids content of the tailings were leading to premature filling of the tailings storage facility, as well as poor water recovery.
Our response
Investigating flow patterns and evaluating design modifications
The need to improve their production performance led AngloGold Ashanti, a sponsor of an AMIRA project for improving thickener technology (AMIRA P266D) at the time, to commission a study on the thickener.
Applying computational fluid dynamics (CFD), we led a project team to investigate the flow patterns in the thickener feedwell and to evaluate design modifications.
Our CFD models showed uneven (asymmetric) flow with poor mixing and jetting of the feed down and out of the feedwell. We found that introducing a feedwell shelf of a suitable size and in the right position would strongly influence the unit's overall performance.
Based on these results, we recommended a number of simple design modifications to dramatically improve the fluid flow. The new design better utilised the feedwell volume, dispersing solids evenly in the upper section and with a uniform discharge into the thickener settling volume.
The results
Better flocculation, cost savings and maximised water use
AngloGold Ashanti was able to save about $100,000 a year just as a result of improved flocculant use at its Sunrise Dam operation.
More significantly, better flocculation led to a higher underflow solids content and a higher yield stress being delivered to the tailings storage facility.
The company was also able to maximise its water use, reduce contaminants in its tailings waste and significantly enhance its tailings storage capacity for further cost savings.