Introduction - Advanced Control and Supervision of Mineral Processing Plants - page 3

and/or using adequate reagents, it is possible to render the valuable minerals air-avid
(aerophilic) and the gangue minerals water-avid (aerophobic). This results in sep-
aration by transferring the valuable minerals to the air bubbles which form a froth
floating on the surface of the pulp, from where it is removed as valuable product
(concentrate).
Final product handling . It normally involves two steps:
1. Dewatering processes , by which the solid particles, either in the concentrate or
the tailings streams, are concentrated by elimination of part of the contained
water, which is recovered for re-use. This is normally done by using thickeners,
although in some cases (concentrates) filters and driers might be necessary to
further decrease the water content.
2. Material transport : concentrate is then transported as thicker pulp to the fi-
nal handling facility for further transportation to the port or smelting facilities,
whereas tails are dumped into ponds in an environmentally friendly manner.
1.2 A Concentration Plant
A mineral concentration plant, called a concentrator or simply a mill, comprises
several units where the above-mentioned operations take place, as depicted in Figure
1.2. In this section, a brief description of these unit operations is provided as an
overview of the processes involved in a concentrator and their interactions. Further
description can be found elsewhere [2-9].
1.2.1 Crushing Circuits
This is the first unit operation after the initial fragmentation provided by under-
ground or open-pit blasting. The mechanisms of size reduction are based on the
slow compression of large particles against rigid surfaces. Crushing is performed in
one or more stages with smaller reduction ratios; i.e. , the ratio feed top-size to prod-
uct top-size. The first stage (primary crushing) is usually done at the mine, reducing
the size of the blasted ore to a level adequate for direct feeding semi-autogenous
mills or convenient for further crushing, when the grinding mill is of a conventional
type. In addition, screens are used before the crusher to minimize packing the crush-
ing chamber by fines or downstream to separate already final-product size material.
The discharge of the secondary and tertiary crushers, normally on the surface, is
usually classified on a screen to produce an oversize stream which is recirculated
to the tertiary crushers and an undersize product that goes to fine ore bins for feed-
ing the concentrator. This final screening eliminates packing of fines in the tertiary
crusher, reduces the production of finely sized material, and thus helps maximize
circuit throughput.