XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3 1311
plant. The present paper will focus on the primary SX cir-
cuit, and more specifically on the recovery of scandium and
the rare earth elements prior their individual separation.
LEACH CIRCUIT PROCESS
DESCRIPTION
Calcination
The demonstration plant calcination is performed using a
continuous rotary kiln processing 10 kg per hour at 950
C for an average of 15 minutes. In this process, calcium
and magnesium carbonates are converted to their respective
oxides and made available for leaching by an ammonium
chloride solution. Approximately 21 wt% of the initial ore
mass is lost during this stage.
Ammonium Chloride Cycle
The ammonium chloride cycle is composed of an ammo-
nium chloride leach circuit followed by a carbonate pre-
cipitation circuit. The carbonate precipitation circuit
regenerates the ammonium chloride solution which is
recycled to the leach circuit. The theoretical framework
and bench scale data supporting the design of the dem-
onstration unit has been published elsewhere (Larochelle,
2022). The system can be described by the overall equations
(M=Mg, Ca, Zn) :
MO(s) +2 NH4Cl(a) ↔ MCl2(a) +2 NH4OH(a) (1)
NH4OH(a) ↔ NH3(g) +H2O (2)
MCl2(a) +CO2(g) +NH4OH(a) ↔
MCO3 +NH4Cl(a) (3)
The demonstration unit presented in Figure 2 contains
three leaching stages with partial dewatering of the solids
followed by a filtration of the residue.
The ammonium chloride pregnant leach solution
(NH4-PLS) containing primarily calcium and magnesium
is sent to the absorber and from the absorber to the crystal-
lizer. The carbonate slurry is filtered and the regenerated
ammonium chloride solution is recycled to the leach cir-
cuit. L3 operated this unit for approximately 11 months
processed approximately 2,400 kg of calcined ore. The
elemental distribution of the carbonate material produced
during a selected two-month period by the demonstration
unit is presented as Figure 3. The ammonium chloride unit
operated continuously in daily campaigns on a 5 days per
week, 8 hours per day basis. Carbonate solids were accumu-
lated in a filter press and representative samples were taken
from the cake during the filter discharge process.
Hydrochloric Acid Leach
The hydrochloric acid leach unit is composed of a cascade
of three 1-hour residence time agitated reactors with tem-
perature controlled at 80 °C. The chemistry of this unit
operation has been described previously by Verbaan et al.,
2017 and is well understood for carbonatite materials. The
system can generally be described by the following reaction:
MxOy +2yHCl → xMCl2y/x +yH2O
L3 operated this unit for approximately 6 months, process-
ing ammonium chloride circuit residue. During the dem-
onstration campaign and following the optimization of the
ammonium chloride operation, it became obvious that the
HCl pregnant leach solution (HCl-PLS) had too much
residual acid, with molarities up to 5 M HCl, for the sub-
sequent solvent extraction circuits. Equipment constraints
at the chosen scale prevented L3 from increasing the sol-
ids content in the leach circuit. Thus, it was decided that
HCl-PLS would be recycled in the leach circuit to mimic
a high solids content. L3 operated the hydrochloric acid
Figure 2. Ammonium chloride cycle block flow diagram
plant. The present paper will focus on the primary SX cir-
cuit, and more specifically on the recovery of scandium and
the rare earth elements prior their individual separation.
LEACH CIRCUIT PROCESS
DESCRIPTION
Calcination
The demonstration plant calcination is performed using a
continuous rotary kiln processing 10 kg per hour at 950
C for an average of 15 minutes. In this process, calcium
and magnesium carbonates are converted to their respective
oxides and made available for leaching by an ammonium
chloride solution. Approximately 21 wt% of the initial ore
mass is lost during this stage.
Ammonium Chloride Cycle
The ammonium chloride cycle is composed of an ammo-
nium chloride leach circuit followed by a carbonate pre-
cipitation circuit. The carbonate precipitation circuit
regenerates the ammonium chloride solution which is
recycled to the leach circuit. The theoretical framework
and bench scale data supporting the design of the dem-
onstration unit has been published elsewhere (Larochelle,
2022). The system can be described by the overall equations
(M=Mg, Ca, Zn) :
MO(s) +2 NH4Cl(a) ↔ MCl2(a) +2 NH4OH(a) (1)
NH4OH(a) ↔ NH3(g) +H2O (2)
MCl2(a) +CO2(g) +NH4OH(a) ↔
MCO3 +NH4Cl(a) (3)
The demonstration unit presented in Figure 2 contains
three leaching stages with partial dewatering of the solids
followed by a filtration of the residue.
The ammonium chloride pregnant leach solution
(NH4-PLS) containing primarily calcium and magnesium
is sent to the absorber and from the absorber to the crystal-
lizer. The carbonate slurry is filtered and the regenerated
ammonium chloride solution is recycled to the leach cir-
cuit. L3 operated this unit for approximately 11 months
processed approximately 2,400 kg of calcined ore. The
elemental distribution of the carbonate material produced
during a selected two-month period by the demonstration
unit is presented as Figure 3. The ammonium chloride unit
operated continuously in daily campaigns on a 5 days per
week, 8 hours per day basis. Carbonate solids were accumu-
lated in a filter press and representative samples were taken
from the cake during the filter discharge process.
Hydrochloric Acid Leach
The hydrochloric acid leach unit is composed of a cascade
of three 1-hour residence time agitated reactors with tem-
perature controlled at 80 °C. The chemistry of this unit
operation has been described previously by Verbaan et al.,
2017 and is well understood for carbonatite materials. The
system can generally be described by the following reaction:
MxOy +2yHCl → xMCl2y/x +yH2O
L3 operated this unit for approximately 6 months, process-
ing ammonium chloride circuit residue. During the dem-
onstration campaign and following the optimization of the
ammonium chloride operation, it became obvious that the
HCl pregnant leach solution (HCl-PLS) had too much
residual acid, with molarities up to 5 M HCl, for the sub-
sequent solvent extraction circuits. Equipment constraints
at the chosen scale prevented L3 from increasing the sol-
ids content in the leach circuit. Thus, it was decided that
HCl-PLS would be recycled in the leach circuit to mimic
a high solids content. L3 operated the hydrochloric acid
Figure 2. Ammonium chloride cycle block flow diagram