Heavy metal removal of intermittent acid mine drainage with an open limestone channel

This study is focused on the influence of a particular open limestone channel (OLC) on the quality of the surface water drained from an intermittent watercourse. The OLC was constructed along a creek surrounded by upstream tailings deposits, in an extensive, abandoned sulfide-mining site, which generates acidic and heavy metals-rich drainage water during the occasional precipitation that occurs. The overall length of the OLC is 1986 m, it has an average slope of 4.6%, and consists of two main segments. The effectiveness of this channel was evaluated through different physico-chemical parameters: pH, electrical conductivity (EC), total solids (TS), and heavy metal concentrations (Al, Fe, Zn, Ni, Cu, As, Cd, and Pb), measured in surface water. A total of 47 water samples were collected in 12 rainfall events, in the period 2005–2009. Moreover, for three different precipitation events, depletion curves of these parameters were constructed. The values of pH and Ca were increased downstream of the channel, related to the alkalinity and calcium release of the OLC and carbonates present in the watershed, whereas the EC, TS, K, Mg, SO 4 2 - , Al, Mn, Fe, Ni, Cu, Zn, As, Cd, and Sb decreased towards the mouth of the creek. The OLC reduced the input of heavy metals into the Mar Menor lagoon by one order of magnitude. According to the results, this kind of constructive solution is effective with regard to mitigating the effects of intermittent acid mine drainage in Mediterranean and semi-arid regions.