Fines may be defined as any material smaller than a specified product size, and “coarse” as any material that is larger. The target 80 percent passing size of the grinding circuit product is a convenient reference point, as it is often used to express the grind size objective. This size is close to the modal value of typical size distributions of ground material, and also roughly approximates the classifier cut size.
The effectiveness of the fines removal system depends on the transportation of material to the classifier. It also depends on the ability of the classification equipment to remove the fines that are presented to it from the circuit, and to return the coarse material to the mill. Immediate and perfect sorting action would result in a circuit product size distribution dependent only on the material fracture characteristics (Austin et al, 1984), and avail the maximum possible amount of mill volume (and applied power) for the breakage of coarse particles. The fraction of fines in the mill hold-up (the “fines inventory”) may therefore be taken as a direct measure of the lack of the system’s fines removal effectiveness. Its complement, the “coarse solids inventory” represents the fraction of the mill volume ….Read more