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Highlights • Present hydrodynamic behavior in five hydraulic reactors for ultra-flocculation. • Estimate agitation using a new mean shear rate based on hydraulic variables. • Shear rate production depends on the pressure drop, vorticy and confinement level of reactor designs. Abstract The efficient use of water has become an important issue in the mining industry, especially in countries where it is located in desert areas with low water reserves, as is the case in Chile. In addition, low ore grades necessitate efforts to recover the maximum amount of minerals in solid–liquid separation processes. Fine particle flocculation is a preliminary stage in various solid–liquid separation processes. The conventional flocculation process is done at low shear rates, ensuring that large flocs remain unbroken. However, it has been seen that the application of high shear rates at the beginning of the process for a short period of time significantly improves the solid removal efficiency, reducing the flocculant dosage and the duration and cost of the process, which is known as ultra-flocculation. This work presents a numerical CFD study of the hydrodynamic behavior in five hydraulic reactors for ultra-flocculation, analyzing the shear rate curve over treatment time, dissipation efficiency and average shear rates. A new mean shear rate, which uses hydraulic variables to estimate the average agitation, is also defined. It was shown that the hydraulic shear rate can be useful for developing better hydraulic designs because it provides a second view, which, added to the shear rate curve over treatment time and effective shear rate, allows a more complete judgment of the performance of the designs. [ABSTRACT FROM AUTHOR]