Water consumption has become an important issue for the mineral processing industry. New projects are demanding an increment of water availability nearby the plants, which are usually located in isolated and very dry land. This situation has lead to an increased effort for recovering the maximum amount of water in the solid-liquid separation process. Thickeners are designed to separate clear and reusable water from concentrate underflow. Conventional feedback control has not been effective in stabilizing the process operation when the characteristics of the feed changes over time, since process dynamics exhibits high non-linearity. This work presents an intelligent control based on an expert system applied to an industrial 125 m diameter thickener, processing 13000 m(3)/h of concentrate containing a 27 % of solids. Main results are a reduction in flocculants consumption and a more stable operation, with few emergency conditions.