Chapter 11 - Screening

Abstract

Minerals of interest exist in nature in the dispersed state, as a separate entity, such as native gold particles in silica rock, or in the combined form, such as nickel sulphide in a host rock. Often because of relative differences in the hardness, friability, and crushability between the mineral and host rocks, minerals can be extracted by repeated crushing and other comminution processes. The particles produced, having different sizes and shapes, can be separated over screens that allow particles that are less than the aperture of the screen to pass through while retaining the others. The chapter describes the design and operation of these screens in detail emphasizing that such separations of mineral constituents can be an efficient and cheap method to concentrate a mineral and to reject the gangue constituents in some mineral ores. The three most important design features of screens are surface of screen and aperture of screen hole, types of screens, and the screen movement. In the metallurgical industry, a distinction is made between screening and sieving. The mechanism of size separation by both is the same, but screening generally applies to industrial scale size separations while sieving refers to laboratory scale operations.