Recovery of critical minerals from secondary sources, such as mineralised waste rock, mine tailings, process waste streams, and low-grade ores, has been recommended as a priority to help meet growing demand for critical minerals in australia and globally (Lambert, 2023). The difficulty is that these sources often have a broad mineralogy, and in the case of post-processing waste, can be significantly modified, which poses design challenges for a centralised hydrometallurgical extraction process. There is a clear need for a robust approach for: (1) rapidly assessing the suitability of secondary sources for leaching activities; and (2) screening the necessary process settings that enable efficient leaching conditions. The problem is that there are a considerable number of process factors that influence leaching efficiency which ultimately influence how suitability can be assessed. The goal for this work was to develop a strategically designed experimental methodology that can be used to rapidly model a multi-dimensional leaching system and estimate performance. This work demonstrated a definitive screening Design of Experiment (DoE) as a primary experimental step for assessing low-grade kaolin as a source of critical minerals. The screening DoE required 28 batch leaching studies which surveyed four continuous process variables: process temperature (22-80C), leaching time (0.5-4 hrs), slurry concentration (5-20 wt per cent), and acid concentration (4-20 wt per cent); and stirring behaviour as a categorical variable (on-bottom and uniform suspension). The critical metal recovery (in mg/kg) was modelled as a response variable to enable preliminary prediction and optimisation. The expected outcome of this approach is to quickly identify which secondary source can be rejected or proceed to more advanced leaching studies, such as response surface methodology.