Fig. 12. The percent of aluminum dissolved as a function of time for various solid/liquid (S/L) ratios at 90 °C using 15 wt.% H2SO
The same behavior is seen for curves 2 and 3 (solid/liquid ratios of 1/8 and 1/10, respectively) except that after the maximum value of leached aluminum is attained, these curves fall, but not as sharply as curve 1. This means that the amount of aluminum leached (after reaching the maximum value) decreases as the solid/liquid ratio decreases (i.e., as the concentration of acid gets greater). Curve 4 represents the mixture of lowest solid/liquid ratio (i.e., 1/12). With the highest amount of acid, curve 4 differs from the previous three curves (1–3) in that the percent of aluminum leached increases with time until it reaches a constant value with no further drop. This behavior is attributed to the fact that increasing the amount of H2SO4 resulted in a dissolution of the basic aluminum sulfate, Al6(OH)10(SO4)4, thus precipitated in experiments 1–3 which contained a lower amount of acid. This behavior disappeared, however, for curve 4, due to the presence of acid in a quantity greater than the stoichiometric value. Fig. 13 displays two extraction curves using 35% and 45% acid concentrations. It was found that extraction increases rapidly at first, and then slows. Also, extraction increases with increasing acid concentration.