Potential use of lignite fly ash for the control of acid generation from sulphidic wastes

In the present paper, the potential use of lignite fly ash in the control of acid generation from sulphidic tailings disposed of at Lavrion, Greece was studied. Long-term laboratory column kinetic tests were performed on tailings containing 27% S, which were homogeneously mixed with various amounts of fly ash, ranging from 10 to 63% w/w. The drainage quality of the columns was monitored over a test period of 600 days. Chemical and mineralogical characterisation of column solid residues was performed after a 270-day test period. The hydraulic conductivity of the mixtures was also measured to evaluate the potential of fly ash to form a low permeability layer. Based on the results, the addition of fly ash to sulphidic tailings, even at the lower amount, increased the pH of the drainage at values of 8.6–10.0 and decreased the dissolved concentrations of contaminants, mainly Zn and Mn, to values that meet the European regulatory limits for potable water. Higher fly ash addition to tailings, at amounts of 31 and 63% w/w also reduced the water permeability of material from 1.2×10−5 cm/sec to 3×10−7 and 2.5×10−8 m/s, respectively.