The influence of the roughness of a plane collecting surface on the amount of the magnetically intercepted deposit in axial high–gradient magnetic separation configuration was studied. It has been experimentally established that capture surfaces with different levels of roughness, i.e. with different friction coefficients, lead to different build–up capacities. Theoretical description is based on the fact that the condition that the friction force exceeds hydrodynamic drag force, i.e. Ff ≥ Fd is satisfied in a region of the capture surface whose width depends on the friction coefficient.