Enhancement of hardpan formation by amending sulphidic tailings with limestone or fly ash
A. Xenidis, E. Mylona and A.D. Harokopou

The potential formation of low-permeability hardpan layers by mixing limestone or lignite fly ash with oxidized sulphidic tailings was investigated under actual field conditions. Field tests covering an area of 900 m2 were implemented in Lavrion, Greece. The field testing area was divided into four equal testpads, which were filled with: (a) Lavrion sulphidic tailings without any amendment (control test); (b) sulphidic tailings covered by a 60-cm-thick layer of tailings homogeneously mixed with 75 kg/t limestone; (c) sulphidic tailings – 75 kg/t limestone mixture having a thickness of 150 cm; and (d) sulphidic tailings covered by a 30-cm-thick layer of tailings homogeneously mixed with 180 kg/t lignite fly ash. After four years of field test operations, cemented layers or hardpan, exhibiting increased resistance to penetration, were formed in the testpads. The hardpan layer in the control test was 
observed at a depth of 65 cm and had a thickness of 30 cm. Limestone and fly ash addition to the oxidized tailings resulted in the formation of hardpan layers at depths of 35 cm and 15 cm respectively. The samples collected from the hardpan layers had paste pH higher than 4.5, as compared to pH 2.0 of the oxidized tailings. Limestone was proved to be more effective than fly ash in neutralizing the acidity and maintaining near-neutral pH conditions within the hardpan. On the other hand, the hardpan samples collected from limestone and fly-ash-amended testpads exhibited similar hydraulic conductivity values in the order of 10–6 m/sec.

Key words: fly ash, hardpan, limestone, sulphidic tailings

Land Contamination & Reclamation, 15 (3), 359-373 (2007)

DOI 10.2462/09670513.697

© 2007 EPP Publications Ltd

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