1238 XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3
includes anthropogenic material stocks currently excluded
from material flow (Lim &Alorro, 2021). Technospheric
mining describes the extraction and reclamation of valu-
able resources from these technospheric stocks (Johansson
et al., 2013 Lim &Alorro, 2021). Johansson et al. (2013)
identified that recovering metals from these stocks has
received greater attention owing to environmental factors
(Johansson et al., 2013). Furthermore, they complement
the traditional production process by contributing to the
market demand (Krook et al., 2011). Additionally, process-
ing a waste stream would reduce the volume of net waste
generated.
Considering the potential supply instability of REEs
to the global market, developing a technology that would
process REEs from alternative sources is essential. A few
studies have been reported on the extraction of REE from
waste streams, which are as follows.
Walawalkar et al. (2016) used inorganic acids (HNO3,
HCl, and H2SO4) to extract REEs from phosphogypsum.
They proposed that the HCl was a more economical option,
and the optimal operating conditions were determined to
be 80°C, a concentration of 1.5 mol/L, and a solid-to-liq-
uid ratio of 1/8 for a duration of 20 minutes (Walawalkar et
al., 2016). Canovas et al. (2019) investigated the leaching
of phosphogypsum with acids and chelating agents. They
attained a REE dissolution above 80% with 3M HNO3
however, this caused a greater portion of the impurities to
dissolve (Cánovas et al., 2019). To address that, Canovas et
al. (2019) utilised a pretreatment step with water to remove
a significant portion of the impurities. Li et al. (2022) stud-
ied the extraction of REE from red mud, an alkaline indus-
trial waste. They employed a pretreatment step using oxalic
acid and dilute HCl to enrich the REE content. After that,
they used 1 mol/L H2SO4 to achieve an REE recovery of
80% at 95°C and a solid-to-liquid ratio of 1:5 mL/g for
3 hours (Li et al., 2022).
Although significant REE recoveries are achieved using
the above methods, they utilise harsh chemicals along with
organic acids. Only a few works explore organic acids on
their own for REE extraction. Gergoric et al. (2018) used
citric acid and acetic acid to leach REEs from NdFeB mag-
net powders. A total REE recovery of 95% was achieved
after 24 h with 1 mol/L acetic acid, while REEs were
leached almost quantitatively after 24 h with 1 mol/L citric
acid at room temperature (Gergoric et al., 2018). It was
also found that the leaching of REEs from NdFeB magnets
is efficient with glycolic and maleic acids (Gergoric et al.,
2019). Ji et al. (2022) used organic acids to recover REE
from the calcination product of a coal coarse refuse. They
attained an REE recovery of approximately 50–60% with
0.05 mol/L of maleic, citric, oxalic, and DL-malic acid after
2 hours (Ji et al., 2022).
Another study involving a two-stage organic acid leach
that utilises 0.8 mol/L oxalic acid and 0.2 mol/L EDTA
was proposed by Lazo et al. (2018) for monazite concen-
trate, as shown in Figure 1. To determine the applicability
of the flowsheet, further test work was carried out for sub-
economical ores by Yamini and Dyer (2023). It was seen
that a REE recovery of 65% was achieved for the monazite
concentrate, and around 40–45% was achieved for low-
grade ores (Lazo et al., 2018 Yamini &Dyer, 2023).
It is essential to understand how this flowsheet behaves
for a wide range of feedstocks to optimise the process and
ensure its broader applicability. This study will focus on
extracting REE from mine tailings to understand further
how this flowsheet behaves for different mineralogies. The
tailings for this study are obtained from a currently oper-
ating REE processing plant. Figure 2 shows the flowsheet
of a conventional REE extraction process, indicating the
source of our feed. The main objective of the study is to
understand the behaviour of acid-crack leach (ACL) tail-
ings in the proposed system by characterising and analysing
its reactivity under different experimental conditions.
Oxalic Acid
Leach
S
L
Alkalisation
EDTA Leach
S
L
Hydroxide
Formation
S
L
Solvent
Extraction
Figure 1. A two-stage organic acid leach process (Lazo et al.,
2018)
includes anthropogenic material stocks currently excluded
from material flow (Lim &Alorro, 2021). Technospheric
mining describes the extraction and reclamation of valu-
able resources from these technospheric stocks (Johansson
et al., 2013 Lim &Alorro, 2021). Johansson et al. (2013)
identified that recovering metals from these stocks has
received greater attention owing to environmental factors
(Johansson et al., 2013). Furthermore, they complement
the traditional production process by contributing to the
market demand (Krook et al., 2011). Additionally, process-
ing a waste stream would reduce the volume of net waste
generated.
Considering the potential supply instability of REEs
to the global market, developing a technology that would
process REEs from alternative sources is essential. A few
studies have been reported on the extraction of REE from
waste streams, which are as follows.
Walawalkar et al. (2016) used inorganic acids (HNO3,
HCl, and H2SO4) to extract REEs from phosphogypsum.
They proposed that the HCl was a more economical option,
and the optimal operating conditions were determined to
be 80°C, a concentration of 1.5 mol/L, and a solid-to-liq-
uid ratio of 1/8 for a duration of 20 minutes (Walawalkar et
al., 2016). Canovas et al. (2019) investigated the leaching
of phosphogypsum with acids and chelating agents. They
attained a REE dissolution above 80% with 3M HNO3
however, this caused a greater portion of the impurities to
dissolve (Cánovas et al., 2019). To address that, Canovas et
al. (2019) utilised a pretreatment step with water to remove
a significant portion of the impurities. Li et al. (2022) stud-
ied the extraction of REE from red mud, an alkaline indus-
trial waste. They employed a pretreatment step using oxalic
acid and dilute HCl to enrich the REE content. After that,
they used 1 mol/L H2SO4 to achieve an REE recovery of
80% at 95°C and a solid-to-liquid ratio of 1:5 mL/g for
3 hours (Li et al., 2022).
Although significant REE recoveries are achieved using
the above methods, they utilise harsh chemicals along with
organic acids. Only a few works explore organic acids on
their own for REE extraction. Gergoric et al. (2018) used
citric acid and acetic acid to leach REEs from NdFeB mag-
net powders. A total REE recovery of 95% was achieved
after 24 h with 1 mol/L acetic acid, while REEs were
leached almost quantitatively after 24 h with 1 mol/L citric
acid at room temperature (Gergoric et al., 2018). It was
also found that the leaching of REEs from NdFeB magnets
is efficient with glycolic and maleic acids (Gergoric et al.,
2019). Ji et al. (2022) used organic acids to recover REE
from the calcination product of a coal coarse refuse. They
attained an REE recovery of approximately 50–60% with
0.05 mol/L of maleic, citric, oxalic, and DL-malic acid after
2 hours (Ji et al., 2022).
Another study involving a two-stage organic acid leach
that utilises 0.8 mol/L oxalic acid and 0.2 mol/L EDTA
was proposed by Lazo et al. (2018) for monazite concen-
trate, as shown in Figure 1. To determine the applicability
of the flowsheet, further test work was carried out for sub-
economical ores by Yamini and Dyer (2023). It was seen
that a REE recovery of 65% was achieved for the monazite
concentrate, and around 40–45% was achieved for low-
grade ores (Lazo et al., 2018 Yamini &Dyer, 2023).
It is essential to understand how this flowsheet behaves
for a wide range of feedstocks to optimise the process and
ensure its broader applicability. This study will focus on
extracting REE from mine tailings to understand further
how this flowsheet behaves for different mineralogies. The
tailings for this study are obtained from a currently oper-
ating REE processing plant. Figure 2 shows the flowsheet
of a conventional REE extraction process, indicating the
source of our feed. The main objective of the study is to
understand the behaviour of acid-crack leach (ACL) tail-
ings in the proposed system by characterising and analysing
its reactivity under different experimental conditions.
Oxalic Acid
Leach
S
L
Alkalisation
EDTA Leach
S
L
Hydroxide
Formation
S
L
Solvent
Extraction
Figure 1. A two-stage organic acid leach process (Lazo et al.,
2018)