In this work, we investigate numerically the mixing characteristics of a tank reactor stirred by a low off-bottom clearance magnetically coupled impeller. We calculate the fully three-dimensional, time-dependent flow field using the Reynolds average form of the Navier-Stokes equations and adopting the sliding mesh approach. Mixing of a scalar species is computed in the Eulerian framework. We compute power consumption, pumping capability, fluid dynamic efficiency, and mixing time to homogeneous distribution from pointwise release of a scalar. We identify relationships useful to optimize the choice of operational parameters. Numerical results are in qualitative agreement with empirical correlations available from the literature and may be used to improve understanding of the mixing processes. The numerical procedure used mimics possible experimental approaches with the advantage of a lower cost. The methodology outlined can be a reference method to derive guidelines for optimization of impeller/tank design and identification of operational parameters.