The Stage 1 DFS assumes a dynamic heap desorption with a 3m stack height. Whilst data exists to suggest a stack height of 6m, or higher, is possible, the Project will look to validate this through the Demonstration Plant prior to adopting this as the Stage 1 Base Case. Agglomerates and 5m heap desorption column completed at ANSTO is shown in Figure 6. Subsequent to the work defining metallurgical extraction parameters applied to desorb REE from the clay mineralisation, additional test work has been completed to quantify the downstream impacts, most notably the impact of more aggressive leach conditions at lower pH (higher acidity), resulting in excessive dissolution of impurity elements, notably aluminium (Al) and iron (Fe). As a result, pH conditions applied in the heap desorption was targeted at pH 2, reducing REE extractions, but importantly substantially reducing the dissolution of Al and Fe, and thereby reducing the reagent consumption required to precipitate out impurity elements to reach the target MREC composition (> 40% REE content). Elevated Al presence in the desorption liquor also results in increased potential for REE precipitation losses in the impurity precipitation circuit. As a result of this, test work has defined that operating the heap desorption at pH 2 provides a fair trade off to maximise REE extraction while managing the impurity load reporting the pregnant leach solution (PLS).
Whilst heap desorption columns have demonstrated successful scale up to 5m and additional test work infers the potential to increase to 6m, and beyond, a larger program of variability columns, cribs and heap desorption test modules of approximately 5,000t will be required to confirm this as viable.
https://wcsecure.weblink.com.au/pdf/IXR/02645488.pdf
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