Cyclones are widely used in chemical and pharmaceutical industries to classify, separate and sort particles in fluid suspensions. They constitute the main device in many industrial and water treatment plants. Therefore, many mathematical studies were concerned about optimizing the required classification energy and maximizing the efficiency, as well as avoiding the rejection of harmful elements into nature through the overflow of the hydro-cyclones. This work presents numerical techniques to solve different mathematic and phenomenological models describing the physics inside a hydro-cyclone and conducts a parametric optimization of this unit operation. The ANSYS suit is used to achieve these objectives. To validate the CFD results, a semi-empirical model has been adopted (Plitt model). Many useful insights were obtained, for instance, the most influencing operating parameter is the inlet solid fraction for the cyclone. This parameter widely affects its efficiency, and for some range of values, the particles may go through the cyclone’s overflow instead of its underflow.