Introduction - Advanced Control and Supervision of Mineral Processing Plants - page 2

terial extracted from a mine is usually highly variable, which imposes serious and
continuous challenges for downstream engineers.
Rock that can be processed at a profit is called ore. To extract the minerals car-
rying the valuable metal from the ore, a combination of separation operations, typi-
cally known as mineral processing or ore beneficiation is required. The objective of
the mineral processing plant is to increase, in an economically viable manner, the
concentration of valuable minerals so that the subsequent metal extraction process
becomes profitable.
This topic will focus on sulfides ore processing, although the same processing
stages can be applied to treat many other minerals. The main operations of a mineral
processing plant are depicted in Figure 1.1 along with the products obtained in each
stage, in terms of the processed mineral.

Port

Final product
handling

Mining Size reduction Classification Concentration

Smelting

Tailings

Figure 1.1 Main operations of a mineral processing plant

Size reduction . Rock fragmentation (comminution) liberates valuable minerals
from the ore matrix (in mineral processing), thereby increasing the surface area for
high reactivity (in hydrometallurgy) and facilitating the particle transport between
unit operations. Comminution is carried out in crushers and grinding mills. Whereas
crushers operate on dry ores, grinding mills mostly work on slurries, which means
that a certain amount of water must be added to the ore before it enters the milling
circuit.
Size separation . Since the comminution processes tend to produce broad size
distribution particles, some might not be the right size for adequate grain libera-
tion, thus requiring further comminution. The separation of adequate-sized particles
(liberated) from still large (locked) particles is done through a size classification pro-
cess. Screens are used for coarse particulate sizing whereas cyclones or mechanical
classifiers are used for fine particles.
Mineral concentration . It is the process of ore enrichment that gets rid of most
of the useless species (gangue) keeping as much as possible of the valuable miner-
als (concentration process). Froth flotation is the most commonly used method for
sulfide separations, whereas gravimetric separation is used for heavy minerals (such
as precious metals, iron oxides, etc. ), with magnetic and electrostatic separation for
industrial minerals and iron oxides. In froth flotation, air bubbles are injected into
an agitated pulp. By adjusting some pulp properties (pH, pulp potential (Eh), etc. )