In this study, the application of models to predict the steady state and dynamic behaviour of the pressure leaching stages at a Base Metal Refinery (BMR) is discussed. Part I of this communication provides background about the context of the study, and presents a complete overview of the process concerned and the model development strategy. The steady state model allows the prediction of the operating temperature and the slurry composition in the different autoclave compartments as a function of pressure, feed rates, and the flow rate of the flash recycle stream. The dynamic response of the temperature and stream compositions to changes in the above mentioned process variables can also be predicted. It has been illustrated how interdependencies between process variables can be determined and an improved understanding of the process can be developed by means of the process models. The importance of controlling the relative leaching rates of digenite and covellite to minimise precious metal leaching, for example, was illustrated by modelling the system behaviour at different operation conditions. (C) 2013 Elsevier Ltd. All rights reserved.