A detailed experimental analysis of the particle-wall collision process in a particle-laden horizontal channel flow was performed using particle tracking velocimetry. The particles used in this study were glass beads with a diameter of 100 and 500 mu m and quartz particles with a size of about 100 mu m. Moreover, the effect of wall material on the collision process was analysed. Special attention was paid to the influence of wall roughness and therefore, untreated stainless steel, polished stainless steel, Plexiglas, and rubber gum were used. It was found that wall roughness considerably alters the rebound behaviour of the particles and causes in average a re-dispersion of the particles, i.e. gravitational settling is reduced. A similar effect was observed for the non-spherical quartz particles and a polished stainless steel wall. The experimental data were used to improve and validate a wall collision model to be used in the frame of the Lagrangian approach. In this model the wall roughness is simulated by assuming that the impact angle is composed of the trajectory angle with respect to the plane wall and a stochastic component caused by wall roughness. A modified normal distribution function was assumed for the roughness angle distribution. All the parameters for the wall collision model, such as restitution coefficient and friction coefficient as functions of the impact angle were obtained from the experiments. The simulations showed a very good agreement with the measurements for the particle rebound properties.