An one-dimensional mathematical model addressing the field of tangential velocities, agitation power and other hydrodynamic features necessary for designing large-size unbaffled agitators with a precession impeller is proposed in this study. The adequacy of the model is confirmed by tests, published data, and lengthy positive operational results for industrial agitators with a volume of up to 1000 m(3), designed for leaching of ore slurries. (C) 2011 Elsevier Ltd. All rights reserved.