Field Trials of Low-Cost Permeable Reactive Media for the Passive Treatment of Circum-Neutral Metal Mine Drainage in mid-Wales, UK

This paper addresses the ability of five low cost adsorbent/reactive materials to remove Zn, Pb and Cd from Fe-poor, circum-neutral pH metal mine water in mid-Wales, UK. Compost, iron ochre, basic oxygen furnace slag (BOS) blended with blast furnace slag, waste shell material and fly ash were used in a series of small-scale passive treatment cells to assess metal removal from mine drainage initially containing, on average, 23.5 mg/L Zn, 550 mu g/L Pb and 50 mu g/L Cd. Treatment plants contained between 2 and 20 kg of reactive media, with a 15 minute residence time and treated up to 1 L/minute. Fly ash from a peat fired power station was found to be the most effective material for metal removal, with over 99.0 Zn, Pb and Cd removed from over woo litres of water. The other materials tested initially achieved high levels of metal removal (with between 75 and 99.9% Zn, Pb and Cd removed), however all of the materials saturated with Zn after less than 200 litres of water had been treated. The results of the pilot-scale field trials can be scaled to demonstrate that a modest sized fly ash treatment cell only 2.7 x 2.7 x 1 metres in size would be sufficient to remove 90% of the total metal load from this mine (10L/minute) for a one year period.