<p>This research develops two predictive mathematical models to predict the carbon dioxide (CO₂) adsorption capacity of a volcanic fly ash from Egypt. This type of fly ash is extremely common in Egypt, which makes the development of such mathematical models extremely useful and significant. The models are developed based on experimental results conducted in the Lab under high pressure high temperature conditions for CO₂ adsorption isotherm development. The lab experiments developed isotherms at 23, 40, 60, and 80&#xa0;°C based on the saturation pressure of CO₂ at these conditions. Using the experimentally developed adsorption isotherms, mathematical models were developed and tested using external data for validation. The first mathematical model was developed to predict CO₂ adsorption capacity in moles as a function of CO₂ pressure and the temperature at which adsorption takes place. The second model predicts the CO₂ adsorption mass per unit mass of fly ash used, at different pressure and temperature conditions. This is extremely important since it can help determine the required fly ash mass in the application to capture a specific amount of CO₂, based on the CO₂ capture facility capacity. The mathematical models were validated using experimental results that were not used in the model development. The models had an average prediction accuracy of 91%, which was extremely high.</p>