3.1.2. Effect of leaching time
Fig. 2 shows the effect of time on rare earths leaching
at 100 °C and 300 °C. It can be seen that for leaching at
100 °C rare earth solubility is maximised after 2 h. At
300 °C, a significant decrease in rare earths leaching was
clear when the reaction time increased beyond 0.5 h. It is
important to note that an increase in the reaction time at
elevated temperature will tend to increase sulfuric acid
losses through volatilization which may cause the reprecipitation
of the rare earths (Da Silva et al., 1997).