In this work the influence of the volumetric fraction of the solid phase on the magnetic filtration efficiency is studied by taking into account the effect of the solid particle concentration in the slurry upon its rheological and magnetic properties. A high gradient magnetic filter (HGMF) cell with transversal configuration is considered, within which the suspension contains small paramagnetic particles of spherical shape and identical from the point of view of their size and magnetic properties (uniformly distributed in the magnetic active space). The maximum recovery conditions are determined by numerically solving the particle trajectory equations, which have been derived by neglecting both inertial and gravitational effects, as well as any kind of particle interactions except for hydrodynamic effects.