XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3 3409
the quantity of NaOH. The results in Figure 2 show that
when the mass ratio (i.e., NaOH: α-spodumene) was 0.5,
the total Li extraction was only 28 ± 1.58% which meant
that the α-spodumene was not totally decomposed as also
evident in the XRD patterns shown in Figure 3. When the
mass ratio increased from 1.5 to 3, the extraction of Li did
not change significantly as expected. This is because the
mass ratio of 1.5 was already stoichiometrically excessive
as predicted by theoretical calculations (i.e., the stoichio-
metric ratio of NaOH: α-spodumene =3: 14) as shown in
Rxns. 1−4 (Han et al., 2022). Besides, the increase of mass
ratio above 1.5 increased the extraction of Al and Si into
the solution resulting in high content of impurities in the
product solution (Figure 2). This result is also in agreement
with the diminishing peaks of analcime and keatite in the
XRD patterns (Figure 3). The X-ray diffractograms pre-
sented in Figure 3 for NaOH-roasted α-spodumene reveals
non-uniform patterns characterized by numerous overlap-
ping peaks, underscoring the intricate nature of the roasting
process. Moreover, the occurrence of structurally distorted
and amorphous silicate material, along with the emergence
of new crystalline phases, is evident from the broadening of
peaks and the appearance of additional peaks in the XRD
patterns (Figure 3 and Table 2) (Baki et al., 2022).
Furthermore, the increase of the ratio of NaOH reac-
tant beyond 1.5 during roasting would also result in high
residual NaOH in solution after leaching. Consequently,
the excessive presence of Na ions in solutions will impede
the Li recovery during downstream purification. Therefore,
further increase of NaOH beyond 1.5 demonstrated mini-
mal impact, suggesting the attainment of an optimal process
threshold with a Li extraction of 77 ± 3.40%. Interestingly,
comparable results were obtained in a similar study involv-
ing hydrothermal conversion of α-spodumene to Li2SiO3
using NaOH solution (Qiu et al., 2022) and the advisable
NaOH/α-spodumene was reported as 1.5. In addition, a
study involving K2SO4 roasting followed by water leach-
ing also reported similar results although high temperature
roasting and complexity of potassium removal from solu-
tion were major drawbacks (Ncube et al., 2022).
Effect of Roasting Temperature
As depicted in Figure 4, a roasting temperature of 250 °C
results in an inefficient extraction of Li from α-spodumene,
yielding a mere 5 ± 1.5% recovery. This low efficiency
can be attributed to the inherent stability of silica spe-
cies, which, despite their reactivity with alkali compounds,
exhibit notably slow reaction rates at lower temperatures.
This lethargy arises from the substantial energy required to
break the robust covalent Si–O bonds (Dove et al., 2008
Fertani-Gmati and Jemal, 2016 Li et al., 2019). However,
at roasting temperatures exceeding ~318 °C, α-spodumene
Figure 1. X-ray diffraction pattern of raw α-spodumene concentrate
the quantity of NaOH. The results in Figure 2 show that
when the mass ratio (i.e., NaOH: α-spodumene) was 0.5,
the total Li extraction was only 28 ± 1.58% which meant
that the α-spodumene was not totally decomposed as also
evident in the XRD patterns shown in Figure 3. When the
mass ratio increased from 1.5 to 3, the extraction of Li did
not change significantly as expected. This is because the
mass ratio of 1.5 was already stoichiometrically excessive
as predicted by theoretical calculations (i.e., the stoichio-
metric ratio of NaOH: α-spodumene =3: 14) as shown in
Rxns. 1−4 (Han et al., 2022). Besides, the increase of mass
ratio above 1.5 increased the extraction of Al and Si into
the solution resulting in high content of impurities in the
product solution (Figure 2). This result is also in agreement
with the diminishing peaks of analcime and keatite in the
XRD patterns (Figure 3). The X-ray diffractograms pre-
sented in Figure 3 for NaOH-roasted α-spodumene reveals
non-uniform patterns characterized by numerous overlap-
ping peaks, underscoring the intricate nature of the roasting
process. Moreover, the occurrence of structurally distorted
and amorphous silicate material, along with the emergence
of new crystalline phases, is evident from the broadening of
peaks and the appearance of additional peaks in the XRD
patterns (Figure 3 and Table 2) (Baki et al., 2022).
Furthermore, the increase of the ratio of NaOH reac-
tant beyond 1.5 during roasting would also result in high
residual NaOH in solution after leaching. Consequently,
the excessive presence of Na ions in solutions will impede
the Li recovery during downstream purification. Therefore,
further increase of NaOH beyond 1.5 demonstrated mini-
mal impact, suggesting the attainment of an optimal process
threshold with a Li extraction of 77 ± 3.40%. Interestingly,
comparable results were obtained in a similar study involv-
ing hydrothermal conversion of α-spodumene to Li2SiO3
using NaOH solution (Qiu et al., 2022) and the advisable
NaOH/α-spodumene was reported as 1.5. In addition, a
study involving K2SO4 roasting followed by water leach-
ing also reported similar results although high temperature
roasting and complexity of potassium removal from solu-
tion were major drawbacks (Ncube et al., 2022).
Effect of Roasting Temperature
As depicted in Figure 4, a roasting temperature of 250 °C
results in an inefficient extraction of Li from α-spodumene,
yielding a mere 5 ± 1.5% recovery. This low efficiency
can be attributed to the inherent stability of silica spe-
cies, which, despite their reactivity with alkali compounds,
exhibit notably slow reaction rates at lower temperatures.
This lethargy arises from the substantial energy required to
break the robust covalent Si–O bonds (Dove et al., 2008
Fertani-Gmati and Jemal, 2016 Li et al., 2019). However,
at roasting temperatures exceeding ~318 °C, α-spodumene
Figure 1. X-ray diffraction pattern of raw α-spodumene concentrate