Particle dispersion and deposition in a horizontal turbulent tube flow have been studied with a Turbulent Diffusion Model. Dispersion and deposition are modelled as the combined process of turbulent diffusion and gravitational settling fluxes. The particle diffusion coefficient is expressed in terms of the fluid diffusivity, taking into account the inertial effect and the crossing trajectories effect. The analytical solution for the particle concentration in a one-dimensional problem between two horizontal plates is found, and is used to calculate the relative deposition between the top and the bottom wall. It is investigated how this relative deposition depends on the particle diameter, the height of the channel and the Froude number. The one-dimensional analytical solution is used to predict the two-dimensional deposition flux in a tube, and it is investigated how this depends on the particle diameter and the Froude number. The expression for the deposition flux contains the characteristic physical parameters of the deposition problem that have not been recognized in earlier work.