Abstract: Process for grinding heterogeneous matrices comprising fragile materials and plastic materials, comprising the steps of: (i) introducing in a mill or similar device a heterogeneous matrix comprising plastic materials and fragile materials of variable dimension; (ii) applying, by suitable moving actuator means, kinetic energy to said heterogeneous matrix, by projecting the materials of the matrix at high speed against suitable fixed stop means provided on said mill; (ill) proceeding to grinding under the effect of impacts occurring between the material projected by the actuator means and the material accumulated on said stop means; (iv) discharging the portion of processed material reduced under a prefixed maximum diameter, characterized in that said stop means are configured so that they can hold removably the material projected against the same in an outer region with respect to the volume interested by the movement of said actuator means.