The addition of alkaline substances is a technique commonly used to prevent acid production generated
by the weathering of sulphide-rich sludge. In this work, we show the effectiveness of fly ash, a waste of
coal combustion, as an acid neutralizing residue, by means of the construction of a leaching saturated
column fills with sulphide sludge and fly ash. In addition, in order to understand the behaviour of both
wastes inside the column, a fly ash leaching test (leachates reach a pH>10) and two flow-through
experiments at pH 9 were carried out to calculate oxidative dissolution rates of pyritic sludge in presence
of the fly ash