Separación Por Gravedad

Physical Separation in Science and Engineering, 2003, Vol. 12, No. 1, pp. 31–48

GRAVITY SEPARATION: OLD TECHNIQUE/NEW METHODS
ANDREW FALCONER*
Senior Metallurgist, Lakefield Oretest Ltd, 12, Aitken Way, Kewdale, 6015, Australia
(Received 15 October 2002; Revised 7 January 2003; Accepted 9 January 2003) A comparative review of various types of the main gravity separation devices, both in therecent past and present is presented. The application of each device is discussed in turn, with details of the variables involved and the respective advantages and disadvantages of the separators, together with explanatory diagrams illustrating the processes. Keywords: Gravity concentration; Jig; Spiral; Centrifugal separation; Shaking table; Cone

INTRODUCTION Gravity separation, which relieson the difference in specific gravities of minerals, is one of the oldest techniques for separating minerals. The method has the attraction of generally low capital and operating costs which together with the lack of chemicals and excessive heating requirements means it is generally environment friendly. Over the last 25 years new gravity separation equipment has enhanced these factors, such thatwherever possible gravity separation is a preferred technique. In Australia, where the traditional user is the mineral sands industry, other hard rock minerals such as tantalum and tin are being recovered successfully using gravity separation. In this article, the following gravity separation methods will be discussed:
. . . . . .

Jigs—conventional, in line pressure and centrifugal Pinchedsluices—trays and cones Spirals—wash water and wash waterless Shaking tables—wet and air Fine particle separators—Falcon and MGS Gravity/sizing—hydrosizers and cyclones

A brief history, followed by the separation principle used precedes an itemised list of the variables, advantages and disadvantages of each separation device. A diagram of the separation action is also given in each case.
*E-mail:andrewf@oretest.com.au ISSN 1478-6478 print/ISSN 1478-6486 online ß 2003 Taylor & Francis Ltd DOI: 10.1080/1478647031000104293

32

A. FALCONER

JIGS Conventional jigs have been in use for well over a century. New developments include the In Line Pressure jig and the Kelsey jig, the latter of which incorporates centrifugal motion. In principle, separation of particles of differing specificgravity is effected in a bed resting on a ragging screen. The bed is fluidised by a vertical pulsating motion created by a diaphragm and an incoming flow of hutch water, coupled with a bed of intermediate specific gravity particles or ‘‘ragging’’. The pulsating and dilating action of this motion on the bed causes the heavier particles (high specific gravity and size) to sink into and through theragging to form a concentrate underflow, and lighter and smaller particles to form a tailing overflow (Fig. 1).

(a)

feed

ragging screen tails diaphragm ragging coarse low SG coarse high SG fine high SG fine low SG hutch water valve

spigot

cons

(b)

start AT POINT A

differential initial acceleration AT POINT B

hindered settling AT POINT C

consolidation trickling ATPOINT D

C upward flow B A D time downward flow pulsation suction

FIGURE 1 (a) Cross section of a typical jig. (b) The jigging cycle.

GRAVITY SEPARATION

33

Conventional Jigs There are many variations of a conventional jig; one example is the Russell. This consists of two parallel feed boxes each of which discharges into two sets of cells arranged in series. The feed slurry flows overthe two hutches where it is subjected to the forces described above. The high specific gravity (SG)/coarse grains pass through the ragging and screens into the hutches where they are removed as an underflow concentrate, while the remainder of slurry discharges into an overflow launder as tailings. Variables
– Pulse rate (increased rate causes greater bed dilation and concentrate weight take, up...