the first stage is called "roughing", which produces a "rougher concentrate". the objective is to remove the maximum amount of the valuable mineral at as coarse a particle size as practical. the finer an ore is ground, the greater the energy that is required, so it makes sense to fine grind only those particles that need fine grinding. complete liberation is not required for rougher flotation, only sufficient liberation to release enough gangue from the valuable mineral to get a high recovery.