Separation in Streaming Currents

Abstract

The term “film sizing” has been defined as “Reverse classification; sorting of mineral particles on such flattish surfaces as sluices and shaking tables in accordance with the sizes of the particles moved by a flowing film of water, which exercises transporting force proportional to the cross-section exposed to flow”.¹ The thrust exerted by the streaming water can be used to size homogeneous sand, to wash particles of a light mineral away from those of a heavier species, or to separate particles of similar mass but different shape. In ore treatment all three effects are produced together unless pre-treatment has modified one or more of the operating factors—particle size, density and shape. This streaming force is manipulated in various ways and in several types of machine. The appliances used to separate heavy minerals from relatively light ores depend mainly upon the work done by water as it encounters ore particles while flowing down an inclined plane. This plane may be smooth, rough, or riffled; gently or steeply inclined; stationary or mobile. Instead of a plane, concave or convex surfaces may be used, or compound planes. Flow may be quiet or turbulent, steady or intermittent, and elements of vertical or centrifugal motion can be introduced. This section discusses the forces that act upon particles moved by a layer of water as it flows down an inclined plane.