3412 XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3
modest yields of 13 ± 0.94%, 56 ± 2.16%, and 68 ± 1.87%,
respectively (Figure 5). Notably, a roasting duration of 2
hours yields a Li extraction of 77 ± 1.54%, and further
increase of roasting time did not yield a significant differ-
ence in Li extraction (Figure 5). Hence, a roasting dura-
tion of 2 hours was selected as the optimum value. This is
due to the slow reaction rate of alkali compounds to break
the Si–O bonds in the intact structure of α-spodumene.
This further provides evidence that the ion-exchange reac-
tions involving Li and Al in α-spodumene with Na are
kinetically slow. A similar phenomenon was observed with
the reaction of K2SO4 with α-spodumene (Ncube et al.,
2021). Furthermore, following a specific level of Li ion
exchange with Na, there is a transition in the mechanism
to the reconstructive transformation of α-(Li)-spodumene
into keatite. This transition is substantiated by a reduction
in both α-spodumene and NaOH levels, aligning with
the emergence of keatite. As a result, the NaOH-roasting
reaction occurs at a comparatively lower temperature com-
pared to values documented in the existing literature when
α-spodumene reacts with alternative reagents (Rosales et
al., 2019 Ncube et al., 2021). This underscores a signifi-
cant advantage of the present process.
Leaching Optimization
Effect of Stirring Rate
Stirring speed stands as a pivotal parameter exerting influ-
ence on nearly all chemical or electrochemical leaching
reactions. This influence is underscored by the fact that the
thickness of the boundary layer enveloping a solid particle
in the lixiviant is contingent upon the degree of agitation.
Elevating the stirring speed yields an augmented shear rate
within the solution, ultimately resulting in the thinning
of the film layer. This attenuation of the film layer serves
to facilitate diffusion and heighten the mass transfer rate
through the film diffusion layer, a phenomenon widely
acknowledged in the field (Makanyire et al., 2016 Faraji
et al., 2022). In our investigation, the impact of stirring
rate was systematically assessed, encompassing scenarios of
no stirring, 100 rpm, 200 rpm, 300 rpm, and 400 rpm,
as graphically depicted in Figure 6. The leaching process
transpired over a 2-hour duration employing a solid-to-
liquid ratio of 1% and room temperature (i.e., 23 °C). The
results distinctly indicate that the absence of stirring fails to
impart adequate suspension of Li ions to the slurry, while
stirring speeds ranging from 100 rpm to 400 rpm yield
analogous kinetics with no observable significant dispari-
ties, as evidenced by the 95% confidence intervals of recov-
ery values (Figure 6). This shows that the Li dissolution
reaction operates independently of diffusion at 2 hours and
is primarily governed by chemical kinetics over the period
studied (Faraji et al., 2022).
Effect of Solid-to-Liquid Ratio
The solid-to-liquid (S/L) ratio plays a pivotal role in shap-
ing the stoichiometric balance of reactants, exerting a direct
Figure 5. Effect of roasting duration on Li extraction for 1.5:1 NaOH-to-α-spodumene
at a roasting temperature of 325 °C
modest yields of 13 ± 0.94%, 56 ± 2.16%, and 68 ± 1.87%,
respectively (Figure 5). Notably, a roasting duration of 2
hours yields a Li extraction of 77 ± 1.54%, and further
increase of roasting time did not yield a significant differ-
ence in Li extraction (Figure 5). Hence, a roasting dura-
tion of 2 hours was selected as the optimum value. This is
due to the slow reaction rate of alkali compounds to break
the Si–O bonds in the intact structure of α-spodumene.
This further provides evidence that the ion-exchange reac-
tions involving Li and Al in α-spodumene with Na are
kinetically slow. A similar phenomenon was observed with
the reaction of K2SO4 with α-spodumene (Ncube et al.,
2021). Furthermore, following a specific level of Li ion
exchange with Na, there is a transition in the mechanism
to the reconstructive transformation of α-(Li)-spodumene
into keatite. This transition is substantiated by a reduction
in both α-spodumene and NaOH levels, aligning with
the emergence of keatite. As a result, the NaOH-roasting
reaction occurs at a comparatively lower temperature com-
pared to values documented in the existing literature when
α-spodumene reacts with alternative reagents (Rosales et
al., 2019 Ncube et al., 2021). This underscores a signifi-
cant advantage of the present process.
Leaching Optimization
Effect of Stirring Rate
Stirring speed stands as a pivotal parameter exerting influ-
ence on nearly all chemical or electrochemical leaching
reactions. This influence is underscored by the fact that the
thickness of the boundary layer enveloping a solid particle
in the lixiviant is contingent upon the degree of agitation.
Elevating the stirring speed yields an augmented shear rate
within the solution, ultimately resulting in the thinning
of the film layer. This attenuation of the film layer serves
to facilitate diffusion and heighten the mass transfer rate
through the film diffusion layer, a phenomenon widely
acknowledged in the field (Makanyire et al., 2016 Faraji
et al., 2022). In our investigation, the impact of stirring
rate was systematically assessed, encompassing scenarios of
no stirring, 100 rpm, 200 rpm, 300 rpm, and 400 rpm,
as graphically depicted in Figure 6. The leaching process
transpired over a 2-hour duration employing a solid-to-
liquid ratio of 1% and room temperature (i.e., 23 °C). The
results distinctly indicate that the absence of stirring fails to
impart adequate suspension of Li ions to the slurry, while
stirring speeds ranging from 100 rpm to 400 rpm yield
analogous kinetics with no observable significant dispari-
ties, as evidenced by the 95% confidence intervals of recov-
ery values (Figure 6). This shows that the Li dissolution
reaction operates independently of diffusion at 2 hours and
is primarily governed by chemical kinetics over the period
studied (Faraji et al., 2022).
Effect of Solid-to-Liquid Ratio
The solid-to-liquid (S/L) ratio plays a pivotal role in shap-
ing the stoichiometric balance of reactants, exerting a direct
Figure 5. Effect of roasting duration on Li extraction for 1.5:1 NaOH-to-α-spodumene
at a roasting temperature of 325 °C