XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3 2277
significant challenges in processing to separate them (Anon
2024 Sime 2018 Trant 2018 Galt 2017 Gupta and
Krishnamurthy 2005 Gupta 1992).
As natural materials, REE deposits usually come in
two different types. Some REE sources are attached to ion-
exchangeable clays while others are crystallized as REMs.
Most of the HREEs that are naturally present are adsorbed
on kaolinite and halloysite clays of which both have the
same chemical formula of Al2Si2O5(OH)4. There are six
different types of deposits that REMs can be found in:
carbonatites, peralkaline igneous systems, magmatic mag-
netite-hematite bodies, iron oxide-copper-gold deposits,
xenotime-monazite accumulations in mafic gneiss, and
monazite-xenotime-bearing placer deposits. Furthermore,
REMs can be classified into four distinct types and are
named according to the anion that the rare-earth cations
are bound to: rare-earth oxides (REOs), phosphates (REPs),
carbonates (RECs), and silicates (RESs) as noted by Young
(2023), Sime (2018), Trant (2018), Galt (2017), and van
Gosen et al. (2017).
Jordens et al. (2013). Young et al. (2023) and Young
(2023) mentioned that REMs and their compositions
depend on the location within the deposit as well as fac-
tors like depth, aeration, hydration, age, and weathering
among many others. Additionally, the REMs are frequently
combined with other cations and consist of a minimum
of two REEs leading to the creation of solid solutions
with varying levels of purity and content. There are about
250 REMs with examples including knopite [(Ce,Ca,Na)
(Ti,Fe)O3] and loparite [(Ce,Ca,Sr,Na)2(Ti,Ta,Nb)2O6]
as REOs, xenotime [(Y,Dy,Yb,Er,Gd)PO4] and monazite
[(Ce,La,Nd)PO4] as REPs, bastnaesite [(Ce,La,Y)CO3F]
and parasite [(Ce,La,Nd)2Ca(CO3)3F2] as RECs, and alla-
nite [(Ce,La,Y,Ca)2(Al,Fe)3(SiO4)3OH] and gadolinite
[(Ce,La,Nd,Y)2FeBe2Si2O10] as RESs.
RESs are interesting because they are more of challenge
(LeVier 2023 and Pickarts 2023). Ignoring issues like pro-
ducing slimes which can be problematic in mineral separa-
tions, they also have varied chemistries due to their REE
content but also the type of silicate present. First, with the
two examples just noted, allanite has a Si:O ratio of 0.25
whereas gadolinite has a ratio of 0.2. This difference likely
has an impact on flotation chemistry due to differences in
coordination number (CN) and lanthanide contraction
(LC) as known to occur for the other REMs (Galt, 2017
Trant, 2018, Sime, 2018). In this regard, it is known that
RECs have CNs of 10, REPs have CNs of 8 and 9, and
REOs have CNs of 6 and 7. Furthermore, per LC, REE
ionic radii decrease with increasing atomic number but also
with decreasing CN.
The objective of this research is to determine if this
behavior applies to RESs and if it changes with RES type.
All of these phenomena combine to complicate the extrac-
tion and treatment of rare earth silicates, thereby render-
ing their processing a formidable undertaking (Nageswara
2014 Fleet and Lui 2001).
Rare Earth Minerals Flotation
Studies on appropriate collectors for rare earth flotation
have determined that hydroxamates (HA) are the predomi-
nant collectors employed for rare-earth extraction. Octyl
hydroxamate (OHA) is demonstrated to be superior to
oleate, a fatty acid (FA) collector, as proven by Pradip and
Fuerstenau in their studies conducted in 1983 and 1991.
This research has established the adsorption behavior of
the two collectors on different mineral surfaces, and this
knowledge was crucial in optimizing the recovery process.
Studies often concentrate on two specific rare earth miner-
als: monazite (Ce, La, Nd, Th) PO4) and bastnaesite ((Ce,
La)CO3F). As an illustration, Pavez et al. (1996) examined
the ability of monazite and bastnaesite samples to float-
ing when sodium oleate and potassium octyl-hydroxamate
were present. Monazite exhibited a 90% recovery rate when
exposed to oleate at a pH of 3, while hydroxamate resulted
in approximately 70% recovery at a pH of 5. In contrast,
the recovery of bastnaesite was marginally greater when
using hydroxamate (almost 90% at pH 10) compared to
oleate (nearly 90% at pH 9).
Nevertheless, the declining quality of modern REE ores
in terms of both grade and liberation size poses a challenge
for flotation using HA and FA collectors. This is mostly
owed to the low recovery rates, which often hover around
60% or less (Pavez et al., 1996 Pradip and Fuerstenau
1991). Presently, efforts to enhance recoveries are primarily
focused on developing novel collectors through modifica-
tions such as altering the head group’s functionality and
size, the length and type of the organic tail, and the number
of tails. This includes, but is not restricted to, the utilization
of salicylhydroxamic acid (SHA), N-3 dihydroxy naphtha-
lene-2-carboxamide (H2O5), and an oleate/hydroxamate
derivative (sarcosinate). An investigation conducted by Xia
et al. (2014) analyzed the impact of three hydroxamates
(salicyl, benzoyl, and H2O5) on the retrieval of rare earth
elements using a sequence of microflotation tests. In addi-
tion, dual collector systems were employed to compare
them with the results obtained from the single collector.
The tested ore primarily consisted of Ce, La, Nd, Nb, Zr,
and Y oxides. The authors claimed that SHA resulted in
the highest recoveries of light rare earth elements (LREE),
closely followed by H2O5, with recoveries reaching up to
significant challenges in processing to separate them (Anon
2024 Sime 2018 Trant 2018 Galt 2017 Gupta and
Krishnamurthy 2005 Gupta 1992).
As natural materials, REE deposits usually come in
two different types. Some REE sources are attached to ion-
exchangeable clays while others are crystallized as REMs.
Most of the HREEs that are naturally present are adsorbed
on kaolinite and halloysite clays of which both have the
same chemical formula of Al2Si2O5(OH)4. There are six
different types of deposits that REMs can be found in:
carbonatites, peralkaline igneous systems, magmatic mag-
netite-hematite bodies, iron oxide-copper-gold deposits,
xenotime-monazite accumulations in mafic gneiss, and
monazite-xenotime-bearing placer deposits. Furthermore,
REMs can be classified into four distinct types and are
named according to the anion that the rare-earth cations
are bound to: rare-earth oxides (REOs), phosphates (REPs),
carbonates (RECs), and silicates (RESs) as noted by Young
(2023), Sime (2018), Trant (2018), Galt (2017), and van
Gosen et al. (2017).
Jordens et al. (2013). Young et al. (2023) and Young
(2023) mentioned that REMs and their compositions
depend on the location within the deposit as well as fac-
tors like depth, aeration, hydration, age, and weathering
among many others. Additionally, the REMs are frequently
combined with other cations and consist of a minimum
of two REEs leading to the creation of solid solutions
with varying levels of purity and content. There are about
250 REMs with examples including knopite [(Ce,Ca,Na)
(Ti,Fe)O3] and loparite [(Ce,Ca,Sr,Na)2(Ti,Ta,Nb)2O6]
as REOs, xenotime [(Y,Dy,Yb,Er,Gd)PO4] and monazite
[(Ce,La,Nd)PO4] as REPs, bastnaesite [(Ce,La,Y)CO3F]
and parasite [(Ce,La,Nd)2Ca(CO3)3F2] as RECs, and alla-
nite [(Ce,La,Y,Ca)2(Al,Fe)3(SiO4)3OH] and gadolinite
[(Ce,La,Nd,Y)2FeBe2Si2O10] as RESs.
RESs are interesting because they are more of challenge
(LeVier 2023 and Pickarts 2023). Ignoring issues like pro-
ducing slimes which can be problematic in mineral separa-
tions, they also have varied chemistries due to their REE
content but also the type of silicate present. First, with the
two examples just noted, allanite has a Si:O ratio of 0.25
whereas gadolinite has a ratio of 0.2. This difference likely
has an impact on flotation chemistry due to differences in
coordination number (CN) and lanthanide contraction
(LC) as known to occur for the other REMs (Galt, 2017
Trant, 2018, Sime, 2018). In this regard, it is known that
RECs have CNs of 10, REPs have CNs of 8 and 9, and
REOs have CNs of 6 and 7. Furthermore, per LC, REE
ionic radii decrease with increasing atomic number but also
with decreasing CN.
The objective of this research is to determine if this
behavior applies to RESs and if it changes with RES type.
All of these phenomena combine to complicate the extrac-
tion and treatment of rare earth silicates, thereby render-
ing their processing a formidable undertaking (Nageswara
2014 Fleet and Lui 2001).
Rare Earth Minerals Flotation
Studies on appropriate collectors for rare earth flotation
have determined that hydroxamates (HA) are the predomi-
nant collectors employed for rare-earth extraction. Octyl
hydroxamate (OHA) is demonstrated to be superior to
oleate, a fatty acid (FA) collector, as proven by Pradip and
Fuerstenau in their studies conducted in 1983 and 1991.
This research has established the adsorption behavior of
the two collectors on different mineral surfaces, and this
knowledge was crucial in optimizing the recovery process.
Studies often concentrate on two specific rare earth miner-
als: monazite (Ce, La, Nd, Th) PO4) and bastnaesite ((Ce,
La)CO3F). As an illustration, Pavez et al. (1996) examined
the ability of monazite and bastnaesite samples to float-
ing when sodium oleate and potassium octyl-hydroxamate
were present. Monazite exhibited a 90% recovery rate when
exposed to oleate at a pH of 3, while hydroxamate resulted
in approximately 70% recovery at a pH of 5. In contrast,
the recovery of bastnaesite was marginally greater when
using hydroxamate (almost 90% at pH 10) compared to
oleate (nearly 90% at pH 9).
Nevertheless, the declining quality of modern REE ores
in terms of both grade and liberation size poses a challenge
for flotation using HA and FA collectors. This is mostly
owed to the low recovery rates, which often hover around
60% or less (Pavez et al., 1996 Pradip and Fuerstenau
1991). Presently, efforts to enhance recoveries are primarily
focused on developing novel collectors through modifica-
tions such as altering the head group’s functionality and
size, the length and type of the organic tail, and the number
of tails. This includes, but is not restricted to, the utilization
of salicylhydroxamic acid (SHA), N-3 dihydroxy naphtha-
lene-2-carboxamide (H2O5), and an oleate/hydroxamate
derivative (sarcosinate). An investigation conducted by Xia
et al. (2014) analyzed the impact of three hydroxamates
(salicyl, benzoyl, and H2O5) on the retrieval of rare earth
elements using a sequence of microflotation tests. In addi-
tion, dual collector systems were employed to compare
them with the results obtained from the single collector.
The tested ore primarily consisted of Ce, La, Nd, Nb, Zr,
and Y oxides. The authors claimed that SHA resulted in
the highest recoveries of light rare earth elements (LREE),
closely followed by H2O5, with recoveries reaching up to