XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3 1031
ore properties. Still, these results are in line with what was
obtained using a more standard elemental analysis.
Correlation Between Grade and Surface Liberation
While it is interesting to analyse the grade variability on a
particle-by-particle basis, it is more important to analyse its
correlation with surface liberation. A particle can contain a
large amount of valuable material, yet it may not be accessi-
ble due to poor surface liberation. This makes it inaccessible
for concentration methods that rely on surface properties
to separate the materials of economic value from the waste
materials. Such is the case of processes such as froth flota-
tion, electrostatic separation, ore sorting, among others.
The surface liberation of each particle was plotted
as a function of its iron ore grade, which can be seen in
Figure 4. The figure shows that for all sizes, the ore grade is
higher than its surface liberation. This may be due to pref-
erential breakage that takes place at the softer phase, which
in this case is the gangue (mostly composed by kaolinite).
This trend also suggests that while particles may contain a
high amount of valuable material, they may not report to
the concentrate stream due to their poorly liberated sur-
face. This can be resolved by milling down the particles
to increase surface liberation, which is equipment- and
resource-intensive, or by selecting a comminution strategy
that works more efficiently for this specific ore.
Extend of Liberation and Liberation Curves
Using the methodology described in Image Processing and
Methodology, it was possible to obtain the 3D surface lib-
eration for hundreds of particles in the size range between
1 and 10 mm. As a benchmark, surface liberation was ana-
lysed using the standard method of considering the mass
fraction in a given liberation class (red bars in Figure 5). We
then compare it to number fraction for each liberation class
(blue bars in Figure 5), which we propose captures more
accurately the surface liberation of a given size class.
For instance, in the coarser fractions, relatively few
liberated particles may contribute a significant fraction of
the mass fraction. While this may not be obvious for this
specific ore, since it is a rather high-grade iron ore, it will
become more evident for lower grade ores containing a
mineral of interest which density is much higher than that
of the gangue.
It is also important to consider the unliberated parti-
cles. In any comminution device, it is critical to maximise
production of liberated particles, but to minimise locked
or poorly liberated grains. As the proportion of liberated
particles decreases, the proportion of unliberated grains
increases, and as particle size increases, the proportion of
liberated particles is expected to decrease.
Here, we present a new method for displaying these
data, shown in Figure 6. In this figure, the difference
Figure 4. Surface liberation as a function of iron ore grade for particles in the size
fractions between 1 and 10 mm
ore properties. Still, these results are in line with what was
obtained using a more standard elemental analysis.
Correlation Between Grade and Surface Liberation
While it is interesting to analyse the grade variability on a
particle-by-particle basis, it is more important to analyse its
correlation with surface liberation. A particle can contain a
large amount of valuable material, yet it may not be accessi-
ble due to poor surface liberation. This makes it inaccessible
for concentration methods that rely on surface properties
to separate the materials of economic value from the waste
materials. Such is the case of processes such as froth flota-
tion, electrostatic separation, ore sorting, among others.
The surface liberation of each particle was plotted
as a function of its iron ore grade, which can be seen in
Figure 4. The figure shows that for all sizes, the ore grade is
higher than its surface liberation. This may be due to pref-
erential breakage that takes place at the softer phase, which
in this case is the gangue (mostly composed by kaolinite).
This trend also suggests that while particles may contain a
high amount of valuable material, they may not report to
the concentrate stream due to their poorly liberated sur-
face. This can be resolved by milling down the particles
to increase surface liberation, which is equipment- and
resource-intensive, or by selecting a comminution strategy
that works more efficiently for this specific ore.
Extend of Liberation and Liberation Curves
Using the methodology described in Image Processing and
Methodology, it was possible to obtain the 3D surface lib-
eration for hundreds of particles in the size range between
1 and 10 mm. As a benchmark, surface liberation was ana-
lysed using the standard method of considering the mass
fraction in a given liberation class (red bars in Figure 5). We
then compare it to number fraction for each liberation class
(blue bars in Figure 5), which we propose captures more
accurately the surface liberation of a given size class.
For instance, in the coarser fractions, relatively few
liberated particles may contribute a significant fraction of
the mass fraction. While this may not be obvious for this
specific ore, since it is a rather high-grade iron ore, it will
become more evident for lower grade ores containing a
mineral of interest which density is much higher than that
of the gangue.
It is also important to consider the unliberated parti-
cles. In any comminution device, it is critical to maximise
production of liberated particles, but to minimise locked
or poorly liberated grains. As the proportion of liberated
particles decreases, the proportion of unliberated grains
increases, and as particle size increases, the proportion of
liberated particles is expected to decrease.
Here, we present a new method for displaying these
data, shown in Figure 6. In this figure, the difference
Figure 4. Surface liberation as a function of iron ore grade for particles in the size
fractions between 1 and 10 mm