XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3 43
from an African IAC deposit demonstrating the critical role
of process mineralogy and geometallurgy is described.
For these ores, a combination of automated-SEM-EDS
(QEMSCAN) and QXRD analysis is essential for process
mineralogical analysis, with the QXRD providing insight
into complex and sometimes interlayered clay phases, and
the auto-SEM-EDS also providing information on poorly
crystalline and trace mineral phases. Figure 6a illustrates
the distribution of minerals in material sampled down the
weathering profile for an African IAC deposit. Just below
the soil horizon, the dominant minerals are quartz, goethite
and kaolinite typical of the hard cap in a lateritic deposit.
The material in the middle horizon represents the more
typical IAC consisting here of both non-swelling kaolin-
ite and illite, as well as the swelling clay montmorillon-
ite. Feldspar, muscovite and quartz, and goethite are the
main gangue minerals in this horizon. Towards the base
of the profile overlying bedrock, montmorillonite pre-
dominates as the main clay with lesser kaolinite and illite.
Quartz, feldspar and muscovite also occur in this horizon.
QEMSCAN analysis of unbroken material indicated the
presence of trace primary REE phases such as monazite.
The transition from montmorillonite to the non-swelling
kaolinite and illite with decreasing depth of the weathering
profile represents more extensive weathering with montmo-
rillonite considered an intermediate step in the alteration
sequence (Wu et al., 2023). The greater abundance of feld-
spar is consistent in indicating a lower degree of weathering
and alteration towards the base of the profile.
However, unlike for most conventional ores, the change
in mineralogy across the deposit (Figure 6a) here provides
no information on the REE distribution. To understand
this, the results are complemented with sequential chemi-
cal extraction tests. These tests are designed to indicate
the relative proportion of REE held in the ion exchange-
able fraction, in organic phases, as well as various crystal-
line and amorphous Fe-oxyhydroxides and Mn-oxides.
Through mass balance, the remaining REE held in discrete
0 20 40 60 80 100
Mineral grade (wt.%)
Goethite
Quartz
Kfeldspar
Plagioclase
Chlorite
Muscovite
Montmorillonite
Illite
Kaolinite
Soil
Parent rock
0 20 40 60 80 100
REE distribution (%)
Residue
Crystalline Fe-oxyhydroxides
Amorphous Fe-oxyhydroxides
Organics
Mn-oxides
Ion exchangeable fraction
Soil
Parent rock
Non-swelling clays
Swelling clay
a). b).
Figure 6. Distribution of (a) mineral grades and (b) REE with increasing depth from the top of an ion adsorption REE clay
deposit. The upper sample represents the lateritic horizon, the middle samples represent the clay horizon and the lower
samples represent the saprolitic horizon. Mineral grades were determined using quantitative XRD with heat treatment and
glycolation for clay mineral identification and do not count for the contribution of amorphous, non-crystalline material.
REE distribution was determined using the sequential chemical extraction method of Denys et al. (2021). Data courtesy of
C. Naude
Increasing
depth
(m)
Increasing
depth
(m)
from an African IAC deposit demonstrating the critical role
of process mineralogy and geometallurgy is described.
For these ores, a combination of automated-SEM-EDS
(QEMSCAN) and QXRD analysis is essential for process
mineralogical analysis, with the QXRD providing insight
into complex and sometimes interlayered clay phases, and
the auto-SEM-EDS also providing information on poorly
crystalline and trace mineral phases. Figure 6a illustrates
the distribution of minerals in material sampled down the
weathering profile for an African IAC deposit. Just below
the soil horizon, the dominant minerals are quartz, goethite
and kaolinite typical of the hard cap in a lateritic deposit.
The material in the middle horizon represents the more
typical IAC consisting here of both non-swelling kaolin-
ite and illite, as well as the swelling clay montmorillon-
ite. Feldspar, muscovite and quartz, and goethite are the
main gangue minerals in this horizon. Towards the base
of the profile overlying bedrock, montmorillonite pre-
dominates as the main clay with lesser kaolinite and illite.
Quartz, feldspar and muscovite also occur in this horizon.
QEMSCAN analysis of unbroken material indicated the
presence of trace primary REE phases such as monazite.
The transition from montmorillonite to the non-swelling
kaolinite and illite with decreasing depth of the weathering
profile represents more extensive weathering with montmo-
rillonite considered an intermediate step in the alteration
sequence (Wu et al., 2023). The greater abundance of feld-
spar is consistent in indicating a lower degree of weathering
and alteration towards the base of the profile.
However, unlike for most conventional ores, the change
in mineralogy across the deposit (Figure 6a) here provides
no information on the REE distribution. To understand
this, the results are complemented with sequential chemi-
cal extraction tests. These tests are designed to indicate
the relative proportion of REE held in the ion exchange-
able fraction, in organic phases, as well as various crystal-
line and amorphous Fe-oxyhydroxides and Mn-oxides.
Through mass balance, the remaining REE held in discrete
0 20 40 60 80 100
Mineral grade (wt.%)
Goethite
Quartz
Kfeldspar
Plagioclase
Chlorite
Muscovite
Montmorillonite
Illite
Kaolinite
Soil
Parent rock
0 20 40 60 80 100
REE distribution (%)
Residue
Crystalline Fe-oxyhydroxides
Amorphous Fe-oxyhydroxides
Organics
Mn-oxides
Ion exchangeable fraction
Soil
Parent rock
Non-swelling clays
Swelling clay
a). b).
Figure 6. Distribution of (a) mineral grades and (b) REE with increasing depth from the top of an ion adsorption REE clay
deposit. The upper sample represents the lateritic horizon, the middle samples represent the clay horizon and the lower
samples represent the saprolitic horizon. Mineral grades were determined using quantitative XRD with heat treatment and
glycolation for clay mineral identification and do not count for the contribution of amorphous, non-crystalline material.
REE distribution was determined using the sequential chemical extraction method of Denys et al. (2021). Data courtesy of
C. Naude
Increasing
depth
(m)
Increasing
depth
(m)