Dissolution of gibbsite proceeeds at low pH:
Al(OH)3 + 3 H+
↔ Al3+ + 3 H2O
And at high pH:
Al(OH)3 + OH-
↔ Al(OH)4-
Accordingly, the total Al concentration in water is a function of the pH.
The PHREEQC input file gibbsite.txt calculates
the pH dependent Al concentration.
A number of waters are defined with increasing pH. The Al concentration is adapted to equilibrium with gibbsite.
The figure shows that the Al concentration may become quite high at low and high pH, in fact exceeding the drinking water limit of 0.2 mg Al / L.