Laboratory Sizing Control

Abstract

The response of a particle to mineral processing is influenced to an important degree by its shape — i.e. its ratio of surface to volume. If one gram of a solid of S.G. 1.0 could be crushed into equi-dimensional particles just passing through a 200-mesh sieve these, if cubic, would have a combined area of 674 cm² ; if oblong 562 and if composed of platy flakes some 2,700. A typical mineral sand would have an area of 922 cm². The surface of a particle is, so to speak, the door to its interior. The bigger the surface vis-à-vis volume, the faster is the rate of reaction and the greater its potential (surface) energy. A sphere has the minimum surface for its volume, and a thin flat plate the minimum volume for its surface. This surface is available for:

• (a) Frictional retardation of the particle.

• (b) Acting as a transition area between solid substrate and fluid surroundings of particle.

• (c) Introducing heat or chemicals to the interior of the particle.

• (d) Displaying the contents of the particle.

• (e) Contributing to the pseudo-viscosity of a pulp (total friction per unit volume).

• (f) Stoichiometric reaction.

• (g) Protecting the contents of the particle it encloses.