Yendon – HPA

The initial metallurgical test work on ore from the Yendon deposit showed very positive leach kinetics and recoveries. The test work had 2 main purposes:

  • Mainly to show that the kaolin feed stock could be treated using the traditional HCl leaching process to achieve a minimum 99.99% purity; and
  • Highlight any areas of the process that may impact the test work for the PFS optimisation process.

The test work was extremely successful on both of these fronts:

  • We achieved a 99.995% pure Al2O3 product.
  • The key learnings from the program were all positive:
    • The feed stock leached very quickly and efficiently. The first leach cycle was planned for 8 hours, but more than 70% of the Al2O3 was leached and precipitated in the first 2 hours.
    • Leaching was done at low temperature, 80-85oC and atmospheric pressure.
Element* Assay
Al2O3 (alumina) 99.995%
Iron 21.5 ppm
Sodium 12.3 ppm
Magnesium 6.8 ppm
Calcium 2.6 ppm
Arsenic 2.3 ppm
Zinc 1.6 ppm
Manganese 1.1 ppm
Potassium 0.3 ppm
Gallium   0.2 ppm
Lead 0.2 ppm
Barium 0.2 ppm 
Tungsten 0.1 ppm 
Copper***  < 1 ppm
Silicon***  < 1 ppm 
Boron*** < 1 ppm 
Other**   0.7 ppm

* Analysis were conducted using induced coupled plasma mass spectrometry. Results shown are for elemental assays not the chemical compound the element may be present as. Volatile elements such as Chlorine, Sulphur, Phosphorus, Carbon and Oxygen were not tested as the analysis method was not suitable or the detection limit was insufficiently sensitive.

** includes 51 other elements analysed for whose results were each below 0.1ppm.

*** certain elements were tested for but not detected and have been included at the detection limit of the equipment.

The metallurgical test work conducted as part of the PFS focused on optimising the process parameters to enable the development of the flow sheet. With this being achieved, the focus has turned to maximising the purity level of the HPA with the aim of achieving a 99.999% (5N) purity. This work will be conducted as part of the DFS.