44 XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3
mineral phases is calculated. Only the REE hosted in the
ion adsorption and organic phases are amenable to REE
recovery using ion exchange leaching. Results from these
tests, illustrated in Figure 6b, indicate that most of the REE
are held in residual phases. In the lateritic sample at the top
of the profile, only ~6% of the REE are amenable to recov-
ery through ion exchange. For the middle clay units, up to
20% of the material is amenable to recovery. This decreases
down to 10% REE amenable to recovery in the saprolitic
horizons. Although the total expected recovery from IAC
leaching is expected to be low, when considered for the
individual REE, the potential recovery of the heavy REE
phases is promising since a greater proportion of the heavy
over the light REE appear to be amenable to IAC leaching
as one moves down the leaching profile.
When the SCE results (Figure 6b) are considered in
conjunction with the mineral grades (Figure 6a), it is evi-
dent that those samples with the highest clay contents occur-
ring in the deepest layers of the weathering profile have the
lowest proportion of REE hosted in the ion exchangeable
fraction. To understand this apparent anomaly, one has to
understand the properties of the clay minerals themselves.
In a comparative study of REE adsorption and extraction on
kaolinite, muscovite, illite and montmorillonite, Alshameri
et al. (2019) demonstrated that although montmorillonite
exhibited the highest REE adsorption efficiency, the REE
are extracted more efficiently from kaolinite followed by
illite, montmorillonite and muscovite. This accounts for
the fact that samples with the higher kaolinite content have
a higher proportion of REE (15%) amenable to recovery
through ion exchange leaching, although this should still
be confirmed with standard batch leaching tests. Without
consideration of the mineralogical properties of the ore
including clay mineral identification, it is not possible to
reconcile the expected ion adsorption leaching behaviour.
From a geometallurgical perspective, aiming to use miner-
alogical data to inform mine planning and blending, it is
clear that the clay type must be considered when blending
to create a run of mine ore (in addition to total REE feed
grades, not described here).
CONCLUSIONS
Critical metals are key to the energy transition. These critical
metals are geochemically scarce elements. Above a certain
concentration threshold these elements occur in discrete
minerals, whereas below this threshold they atomically sub-
stitute for other more common elements in the rock-form-
ing minerals (and are often known as refractory material).
This threshold is known as Skinner’s mineralogical barrier
and has important implications for mining and processing,
especially concerning the energy demand for processing.
Process mineralogy and geometallurgy are key enablers to
understanding the characteristics and mitigating the conse-
quences of problems associated with processing ores bear-
ing these geochemically scarce elements.
The problem of Mn (a geochemically abundant metal)
distribution in the Gamsberg Zn (a geochemically scarce
metal) ore was explored through process mineralogy.
Isomorphous substitution of Mn in the sphalerite crystal
lattice causes challenges to Zn concentrate quality. This
cannot be mitigated through conventional flotation opti-
mization strategies and requires ROM ore blending of
Mn-rich and Mn-poor sphalerites. A process mineralogical
and geometallurgical approach was used to develop a train-
ing dataset upon which regression models could be devel-
oped that allowed the prediction of sphalerite composition
based on chemical assays. This allowed the development of
a geometallurgical model mapping sphalerite composition
throughout the Gamsberg North ore body, and a means
of managing complex element deportment through ore
blending.
Weathered crust elution deposited ion adsorption clay
deposits are low-grade deposits hosting REE adsorbed to
minerals such as kaolinite as opposed to REE occurring in
discrete REE minerals. An African IAC deposit case study
was showcased to illustrate how both conventional min-
eralogical analyses (XRD) complemented with sequential
chemical extraction tests were needed to understand the
distribution of the REE down a weathering profile. The
relationship between ion exchange extraction efficiency
and clay mineralogy was also demonstrated, with kaolinite-
rich horizons in the middle of the weathering profile show-
ing the most promise for total REE ion exchange leaching
compared to the montmorillonite at the base of the profile.
This highlights the importance of understanding the pro-
cess mineralogical characteristics of the ore, especially when
considering selective mining or ore blending.
ACKNOWLEDGMENTS
Grateful thanks to Andrea Mulelu and Keshree Pillay for
their help in generating the Gamsberg mineralogy datas-
ets, as well as Vedanta Zinc International for permission
to publish the Zn case study. Grateful thanks are given to
Chad Naude and Jochen Petersen as well as the mining
company sponsoring this research for allowing the use of
unpublished data for the REE case study. Thank you to
the SAIMM for granting permission to reproduce Figure 5
which originally appeared in Price et al. (2023).
mineral phases is calculated. Only the REE hosted in the
ion adsorption and organic phases are amenable to REE
recovery using ion exchange leaching. Results from these
tests, illustrated in Figure 6b, indicate that most of the REE
are held in residual phases. In the lateritic sample at the top
of the profile, only ~6% of the REE are amenable to recov-
ery through ion exchange. For the middle clay units, up to
20% of the material is amenable to recovery. This decreases
down to 10% REE amenable to recovery in the saprolitic
horizons. Although the total expected recovery from IAC
leaching is expected to be low, when considered for the
individual REE, the potential recovery of the heavy REE
phases is promising since a greater proportion of the heavy
over the light REE appear to be amenable to IAC leaching
as one moves down the leaching profile.
When the SCE results (Figure 6b) are considered in
conjunction with the mineral grades (Figure 6a), it is evi-
dent that those samples with the highest clay contents occur-
ring in the deepest layers of the weathering profile have the
lowest proportion of REE hosted in the ion exchangeable
fraction. To understand this apparent anomaly, one has to
understand the properties of the clay minerals themselves.
In a comparative study of REE adsorption and extraction on
kaolinite, muscovite, illite and montmorillonite, Alshameri
et al. (2019) demonstrated that although montmorillonite
exhibited the highest REE adsorption efficiency, the REE
are extracted more efficiently from kaolinite followed by
illite, montmorillonite and muscovite. This accounts for
the fact that samples with the higher kaolinite content have
a higher proportion of REE (15%) amenable to recovery
through ion exchange leaching, although this should still
be confirmed with standard batch leaching tests. Without
consideration of the mineralogical properties of the ore
including clay mineral identification, it is not possible to
reconcile the expected ion adsorption leaching behaviour.
From a geometallurgical perspective, aiming to use miner-
alogical data to inform mine planning and blending, it is
clear that the clay type must be considered when blending
to create a run of mine ore (in addition to total REE feed
grades, not described here).
CONCLUSIONS
Critical metals are key to the energy transition. These critical
metals are geochemically scarce elements. Above a certain
concentration threshold these elements occur in discrete
minerals, whereas below this threshold they atomically sub-
stitute for other more common elements in the rock-form-
ing minerals (and are often known as refractory material).
This threshold is known as Skinner’s mineralogical barrier
and has important implications for mining and processing,
especially concerning the energy demand for processing.
Process mineralogy and geometallurgy are key enablers to
understanding the characteristics and mitigating the conse-
quences of problems associated with processing ores bear-
ing these geochemically scarce elements.
The problem of Mn (a geochemically abundant metal)
distribution in the Gamsberg Zn (a geochemically scarce
metal) ore was explored through process mineralogy.
Isomorphous substitution of Mn in the sphalerite crystal
lattice causes challenges to Zn concentrate quality. This
cannot be mitigated through conventional flotation opti-
mization strategies and requires ROM ore blending of
Mn-rich and Mn-poor sphalerites. A process mineralogical
and geometallurgical approach was used to develop a train-
ing dataset upon which regression models could be devel-
oped that allowed the prediction of sphalerite composition
based on chemical assays. This allowed the development of
a geometallurgical model mapping sphalerite composition
throughout the Gamsberg North ore body, and a means
of managing complex element deportment through ore
blending.
Weathered crust elution deposited ion adsorption clay
deposits are low-grade deposits hosting REE adsorbed to
minerals such as kaolinite as opposed to REE occurring in
discrete REE minerals. An African IAC deposit case study
was showcased to illustrate how both conventional min-
eralogical analyses (XRD) complemented with sequential
chemical extraction tests were needed to understand the
distribution of the REE down a weathering profile. The
relationship between ion exchange extraction efficiency
and clay mineralogy was also demonstrated, with kaolinite-
rich horizons in the middle of the weathering profile show-
ing the most promise for total REE ion exchange leaching
compared to the montmorillonite at the base of the profile.
This highlights the importance of understanding the pro-
cess mineralogical characteristics of the ore, especially when
considering selective mining or ore blending.
ACKNOWLEDGMENTS
Grateful thanks to Andrea Mulelu and Keshree Pillay for
their help in generating the Gamsberg mineralogy datas-
ets, as well as Vedanta Zinc International for permission
to publish the Zn case study. Grateful thanks are given to
Chad Naude and Jochen Petersen as well as the mining
company sponsoring this research for allowing the use of
unpublished data for the REE case study. Thank you to
the SAIMM for granting permission to reproduce Figure 5
which originally appeared in Price et al. (2023).