Many industries such as food, beauty and pharmaceuticals
rely on a specific particle size in order for their product
to excel. This is also true in mining; this blog will discuss the
importance of particle size as it relates to artisanal and small scale gold mining (ASGM) and how the AGC is using particle size distribution to aid their work in Peru.
In the mining industry, large particles (rocks) are taken
from the ground in the form of ore. The ore is then crushed by hand to a more
manageable size before it is milled by a machine. Once the ore is milled to a
fine dust, the gold is liberated. The size of the dust particles can have a
great impact on how much gold a miner can process from their ore.
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Machines like this crush the ore |
The degree of liberation of gold is measured by particle
size. Particle size is measured in ‘mesh’. Screens are stacked in order to
measure the whole range of particles. Very coarse screens are measured in
inches and smaller particles are measured in microns.
A set of sieves/screens (see image below) can be used to measure
the particle size distribution in a sample. Ex: A Chilean mill (as used by the AGC in Burkina
Faso) is 74mm (74 microns). This is important to:
·
Calculate the energy required to do any further
grinding;
·
Determine if liberation size is sufficient;
· Assess the need for an additional classification process to remove oversized particles.
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Particle size distribution analysis in Cholito, Peru |
In Cholito, Peru, at our mercury free processing and
training centre, there is approximately 20 grams of gold exhumed from 1
tonne of ore (20 gr Au/t). This means that approximately 98-99% of the ore that is processed
will be tailings/waste and the remaining 1% is a valuable gold concentrate.
At Cholito we use particle size distribution analysis to:
- · Separate oversized particles coming out of the secondary crushing circuit;
- · Prepare the grinding load at the ball mill to reduce incoming particles at a specific size;
- · Separate fine and coarse fractions at ball mill exit.
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The ball mill exit separates the fine and coarse material |
Particle size distribution in ASGM is an aspect of better practices that allows miners to
be more efficient and reduce and plan additional classification circuits.
For additional information about particle size distribution and gold recovery, see
our YouTube channel for videos on concentration, milling, and Sixto’s seminar series on the topic.