XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3 1831
Hydrometallurgical Processing
The solid-rich product from CFDC separation was diluted
with water and filtered using a vacuum filter to further
remove the phosphoric acid therein, and then the sludge
solid was used to leach REEs and phosphorus in a ther-
mostatic water-bath reactor. After leaching the mixture was
filtered to get the leachate for REEs extraction.
Thermal Processing
As in hydrometallurgical processing, the solid-rich product
of CFDC separation was diluted, filtered, and dried in an
oven under 105°C to get a sludge solid. Then the dried
sludge was mixed thoroughly with activated carbon pow-
der, and the mixture was put in an airtight furnace to go
through a reduction roasting (RR) process with argon as
a purge gas. After that, the RR product underwent an air
roasting (AR) process in a muffle furnace to burn up the
residual carbon. Finally, the AR product was used in leach-
ing test to produce leachate for REE extraction.
Unlike the conventional thermal process fwor phos-
phorus production as shown in formula (1), in the RR pro-
cess, no silica was added to avoid the generation of slag
(CaSiO3) which could lock the REEs and lower the REEs
recovery in subsequent leaching tests. During the thermal-
processing gypsum and phosphates were reduced and thus
resulting in REEs being released from these compounds.
The main chemical reactions taking place in the thermal
processing are as follows:
2CaSO C 2CaO 2SO
4 2 2 "-+CO -++
(800–1000°C) (2)
CaSO 2C CaS 2CO2
4 "-++
(Carbon-to-sulfur mole ratio 2:1 or more) (3)
4REEPO 5C 2REE O P
4 2 3 4 2 "-+5CO -++(4)
4H PO 5C 6H O 5CO
3 4 2 4 2 "-+P --++(5)
Solvent Extraction for REEs
Solvent extraction experiments were conducted using
standard centrifugal contactors. After extensive screening
tests, an innovative solvent extraction system was devel-
oped. The extraction system consists of 0.1 M N,N,N’,N’-
tetraoctyl diglycolamide (TODGA) as solvent, Exxsol D80
(ExxonMobil) as diluent, and 1 M Exxal C8 (ExxonMobil)
as solvent modifier. This extraction system demonstrated
many unique features, as are discussed below.
Figure 1. Laboratory decanter centrifuge continuous testing system [Jang et al, 2023]
Hydrometallurgical Processing
The solid-rich product from CFDC separation was diluted
with water and filtered using a vacuum filter to further
remove the phosphoric acid therein, and then the sludge
solid was used to leach REEs and phosphorus in a ther-
mostatic water-bath reactor. After leaching the mixture was
filtered to get the leachate for REEs extraction.
Thermal Processing
As in hydrometallurgical processing, the solid-rich product
of CFDC separation was diluted, filtered, and dried in an
oven under 105°C to get a sludge solid. Then the dried
sludge was mixed thoroughly with activated carbon pow-
der, and the mixture was put in an airtight furnace to go
through a reduction roasting (RR) process with argon as
a purge gas. After that, the RR product underwent an air
roasting (AR) process in a muffle furnace to burn up the
residual carbon. Finally, the AR product was used in leach-
ing test to produce leachate for REE extraction.
Unlike the conventional thermal process fwor phos-
phorus production as shown in formula (1), in the RR pro-
cess, no silica was added to avoid the generation of slag
(CaSiO3) which could lock the REEs and lower the REEs
recovery in subsequent leaching tests. During the thermal-
processing gypsum and phosphates were reduced and thus
resulting in REEs being released from these compounds.
The main chemical reactions taking place in the thermal
processing are as follows:
2CaSO C 2CaO 2SO
4 2 2 "-+CO -++
(800–1000°C) (2)
CaSO 2C CaS 2CO2
4 "-++
(Carbon-to-sulfur mole ratio 2:1 or more) (3)
4REEPO 5C 2REE O P
4 2 3 4 2 "-+5CO -++(4)
4H PO 5C 6H O 5CO
3 4 2 4 2 "-+P --++(5)
Solvent Extraction for REEs
Solvent extraction experiments were conducted using
standard centrifugal contactors. After extensive screening
tests, an innovative solvent extraction system was devel-
oped. The extraction system consists of 0.1 M N,N,N’,N’-
tetraoctyl diglycolamide (TODGA) as solvent, Exxsol D80
(ExxonMobil) as diluent, and 1 M Exxal C8 (ExxonMobil)
as solvent modifier. This extraction system demonstrated
many unique features, as are discussed below.
Figure 1. Laboratory decanter centrifuge continuous testing system [Jang et al, 2023]