This paper presents results following the application of a sub-optimal control scheme, both through simulation and in situ, from the operation of Section C of the CODELCO-Andina copper concentrator plant. The algorithm permits the determination of the necessary control action at each instant of time in order to maximize a defined plant performance index. The main objective of the algorithm is to maximize the mineral tonnage processed by the section, subject to it not exceeding a predetermined value established for the operation conditions of the mills, while at the same time maintaining constant the mass fraction over 65 mesh (212 [microns]) in the overflow of the hydrocyclones, at a value within the operational requirements of the flotation stage. The performance index is defined in terms of; the percentage of pulp solids fed to the hydrocyclones of each line of ball mills, penalty functions to prevent electric power to the ball mills falling below the lower limit (so as not to enter the overload region), the tonnage processed in the section, and, since water is a scarce resource, a term considering the water added to each sump is also included. The scheme is first studied and adjusted in a simulator of a concentrator plant similar to that used in the industrial application. For plant implementation, a PC software program, denoted CONMOL, is developed in TurboPascal for Windows. This software allows plant applications to be carried out through a communications interface. Finally, the results of two tests performed on Section C of the CODELCO-Andina copper concentrator plant are shown where the control is applied over 3 and 5.5 hours respectively.