The ionic concentrations increased with time or cycles for both
slag samples. It implies that the slag can provide the cations such as
calcium and aluminum constantly for a certain period. Thus, calcium
and aluminum ions might not be the main factor for the slag
exhaustion at the early stage. The initial concentration of aluminum
in the solution of C4 was higher than 10 mg/L and it could be due to
the coating material of the slag. It is known that sodium hydroxide
solution can make the aluminum be dissolved