An engineering model of the particle diffusivity in horizontal hydraulic conveying pipelines is developed. The model is based on a known equation of the turbulent diffusivity for isotropic turbulence. The Kolmogoroff turbulence model is employed. It is assumed that turbulence develops in an equivalent fluid, representing a solid-liquid suspension. The particle diffusivity model takes into account a diffusivity increase with both the particle size and the mean solids concentration. The model has two empirical parameters, which are identified from the experimental data available in the literature. A comparison of the computed solids concentration distributions over the pipe cross-section with those measured demonstrates a high model accuracy in a wide range of slurry flow parameters. (C) 2012 Elsevier Ltd. All rights reserved.