The rational use of water in the mineral processing industry has become an important issue due to the geographical location of many plants. The increase of capacity in many copper concentrators has lead to an increased effort for recovering the maximum amount of water in the solid-liquid separation process. Thickeners work continuously to produce a concentrated underflow and a water overflow free from particulate matter. These equipments are highly nonlinear systems, and practice has shown that standard feedback control has not been very effective in providing consistent operations. In many plants, thickeners operate with poor standards, with high dosages of flocculants, overflows with high fine particles contents and highly variable underflows. This work presents an overview of the current control strategies found in the industry and the literature for controlling the level of sediment and the underflow concentration, and compares them using a calibrated simulator of an industrial thickeners. The phenomenological model is described along the necessary steps for obtaining its parameters from plant data. The analysis of the results points out the weakness of each control strategies, and provides hints on how to improve their performance by using the insight given by the phenomenological model. © 2011 IFAC.