HPa (299.99 per cent a-al2O3) is one of the key materials essential for the energy transition, driven by its use in batteries and LEDs. Rising HPa demand is projected to result in a supply shortfall over the next decade, with significant research and development underway to capitalise on australia's plentiful supply of cheap feed materials such as aluminous clays. While various mineral acids have been successfully used to extract aluminium from kaolin, limited comparative information is publicly available on these acid systems and the implications for producing HPa. In this context, the CSIRO is evaluating different acid systems for HPa through the australian Critical Minerals Research and Development Hub, funded by the australian Government. Kaolin clay was thermally treated to form metakaolin, and subsequent calorimetric data was collected isothermally to evaluate the aluminium leaching kinetics (50, 65 and 80C and various acid concentrations). The activation energies for aluminium extraction using HCI, H2SO4, and HNO3 were calculated to be 114.8, 101.3, and 90.4 kJ/mol, respectively. These values are consistent with concentration-time experiments (within 6 per cent agreement), demonstrating the effectiveness of the calorimetric approach. No significant differences in liquor purity or aluminium extraction were observed for the three acids tested. First-pass crystallisation of the respective pregnant leach aICl3.6H2O (99.94 per cent), al2(SO4)3-17H2O (98.07 per cent), and solutions produced al(NO3)3.9H2O (98.22 per cent) which influences subsequent purification steps. Thermogravimetric analysis and high-temperature X-ray diffraction revealed the salts' decomposition pathways, the intermediate phases formed before transformation to a-al2O3, and conditions for potential acid regeneration. The results are discussed in terms of the purities of precursor salts formed through various processing steps and the alumina yields achieved after salt decomposition. The cost of reagents, the extent and efficiency of acid regeneration, and materials of construction are additional criteria that need to be considered when evaluating different acid routes for producing high purity alumina.