Antofagasta, Chile, has one of the most important deposits of saltpetre in the world, which is called caliche. These deposits are mainly composed of nitrate, halite, sodium anorthite, and quartz. Minor species include anhydrite, glauberite, loeweite, calcite, polyhalite, probertite, and gypsum. Recently, several operations began to use heap leaching for the extraction of saltpetre. Modelling the heap leaching of caliche is not straightforward because of the many minerals and their different dissolution rates. Moreover, caliche may have a large fraction of soluble minerals, approximately 40%, which causes the heap to slump. In this work, we present two models. The first, which is a phenomenological model, is an extension of the model published by Valencia et al. (2008). The system is modelled as a column comprised of N small columns, and in each of these small columns, the height of the solids varies with time when the soluble minerals are dissolved. The liquid in each small column has the same composition (well-stirred reactor). The second model, which is an analytical model, is an extension of that published by Mellado et al. (2009) for low-grade minerals, such as copper and gold, which considers that the leaching phenomenon occurs on different scales of size and time. However, in this work, the time scale at the particle level is based on the Bruner and Tolloczko dissolution model. The objective of this work is to test the suitability of the analytical model as a tool for use in optimisation, for which the model needs to be solved many times. The phenomenological model was used to generate simulated experimental data. The results show that the analytical model may be a useful tool in optimisation. (C) 2011 Elsevier Ltd. All rights reserved.