Screening / Classifiers

Screening and classification are size separation methods used to control the size distribution of particles at various stages in a mineral processing plant. Necessary to enable undersized material to bypass the crushing or grinding circuit and retain over sized particles for further size reduction as well as providing a specific particle size for efficient processing in separation and concentration systems.

Screening consists of a hard perforated surface with fixed dimension holes throughout. Material is introduced to the screen surface and particles smaller than the hole size fall through the screen, with the oversize particles staying on top and being discharged. Screening is generally reserved for particle sizes above 0.5 mm. Typical screens used are grizzlies (rough screening), vibratory screens, gyratory screens and revolving screens (trommel).

Classification methods use the principle that particles of the same density but of different sizes settle in a fluid at a different rate. Classification is usually carried out at particle size too fine to sort using screening methods. Typcial classifiers used are sedimentation classifiers, hydraulic classifiers, spiral classifiers and hydroclones.

- W.S Tyler, Sandvik Mining and Construction, FLSmidth Minerals, Metso Minerals images.