18
Q. T. Lai et al.
Fig. 3 Effect of time on the leaching efficiency (2 mol/L HCl, 25 °C). (Color figure online)
°C, respectively. The results for REE dissolution with respect to leaching time were
depicted in Fig. 3. Five minutes leaching provided notable REE leaching efficiency,
for example, scandium (31%) and yttrium (41%). The leaching efficiency was slightly
increased when the reaction time increasing up to 60 min. The leaching efficiency of
scandium and yttrium after 60 min leaching was 33% and 42%, respectively. Beyond
60 min, the dissolution of scandium and yttrium was negligible. Hence, the proper
period targeted REE leaching from the FA sample was selected as 60 min.
Effect of HCl Concentration
The effects of HCl concentration on scandium and yttrium leaching were investigated. The concentration of HCl was varied between 1.5–4 mol/L. The condition
for time and temperature was at 60 min and 25 °C, respectively. Leaching efficiency
of scandium and yttrium slightly increased, 30–33% for scandium and 40–41% for
yttrium, when the HCl concentration increased from 1.5 to 4 mol/L (Fig. 4). However,
the higher concentration of HCl used lead to the higher possibility of precipitation
and gel formation. Therefore, the concentration of HCl at 3 mol/L was selected for
subsequent experiments.
Effect of Temperature
Experiments were operated to observe the influence of temperature on REE leaching
in 3 mol/L HCl for 60 min. The leaching yield was studied between the temperature
Q. T. Lai et al.
Fig. 3 Effect of time on the leaching efficiency (2 mol/L HCl, 25 °C). (Color figure online)
°C, respectively. The results for REE dissolution with respect to leaching time were
depicted in Fig. 3. Five minutes leaching provided notable REE leaching efficiency,
for example, scandium (31%) and yttrium (41%). The leaching efficiency was slightly
increased when the reaction time increasing up to 60 min. The leaching efficiency of
scandium and yttrium after 60 min leaching was 33% and 42%, respectively. Beyond
60 min, the dissolution of scandium and yttrium was negligible. Hence, the proper
period targeted REE leaching from the FA sample was selected as 60 min.
Effect of HCl Concentration
The effects of HCl concentration on scandium and yttrium leaching were investigated. The concentration of HCl was varied between 1.5–4 mol/L. The condition
for time and temperature was at 60 min and 25 °C, respectively. Leaching efficiency
of scandium and yttrium slightly increased, 30–33% for scandium and 40–41% for
yttrium, when the HCl concentration increased from 1.5 to 4 mol/L (Fig. 4). However,
the higher concentration of HCl used lead to the higher possibility of precipitation
and gel formation. Therefore, the concentration of HCl at 3 mol/L was selected for
subsequent experiments.
Effect of Temperature
Experiments were operated to observe the influence of temperature on REE leaching
in 3 mol/L HCl for 60 min. The leaching yield was studied between the temperature