The technological process of separating and dividing friable mixtures using separating units is one of the most important stages in the production of products and raw materials in various branches of the national economy. To establish the major parameters of the process and ranges of their change, the author of the article has developed a special model and provides its analytical solution for deriving new criteria for separating friable mixtures. The author has obtained dependencies for calculating the particle separation and withdrawal coefficient, which are linked with the parameters of the unit’s work and physical-mechanical properties of friable mixtures.