Critical particles, also known as ore particles, generally refer to 30-50mm lumps of ore that easily form in the autogenous mill during grinding due to the small quantity of medium and coarse particles in the ore. These lumps are too light to serve as grinding media and cannot be discharged through the grate openings as grinding products. These lumps (critical particles) gradually accumulate in the mill, occupying mill volume, leading to decreased autogenous mill output, increased unit power consumption, and over-grinding. The main measures to eliminate or prevent the accumulation of critical particles in the mill are as follows: (1) Opening a “gravel window” to draw critical particles out of the mill, which can be used as gravel media in a gravel mill or treated separately. (2) Using semi-autogenous grinding, i.e., adding large steel balls (100-150mm in diameter) with a filling rate of 5%-8% into the autogenous mill to supplement the insufficient energy of the large lumps as grinding media and to grind the critical particles. (3) The autogenous grinding-ball milling-crushing process is adopted, namely autogenous open-circuit grinding, which draws out the material on the discharge cylinder screen, and after fine crushing and ball milling, it is combined with the undersize product. This is the so-called A-B-C process.