A continuous pilot-scale system using coal-mine drainage sludge to treat acid mine drainage contaminated with high concentrations of Pb, Zn, and other heavy metals

Highlights: ► Coal mine drainage sludge can effectively neutralize and treat the acidic drainage for a long time. ► We suggest that the continuous pilot system having CMDS can not only high removal efficiencies, but also high total rates for all heavy metals. ► The pilot system can have a much higher Zn(II) loading rate than other referenced systems such as wetland coupled with algal mat and anoxic limestone drain. - Abstract: A series of pilot-scale tests were conducted with a continuous system composed of a stirring tank reactor, settling tank, and sand filter. In order to treat acidic drainage from a Pb–Zn mine containing high levels of heavy metals, the potential use of coal-mine drainage sludge (CMDS) was examined. The pilot-scale tests showed that CMDS could effectively neutralize the acidic drainage due to its high alkalinity production. A previous study revealed that calcite and goethite contained in CMDS contributed to dissolutive coprecipitation and complexation with heavy metals. The continuous system not only has high removal efficiencies (97.2–99.8%), but also large total rate constants (Ktotal, 0.21–10.18 h−1) for all heavy metals. More specifically, the pilot system has a much higher Zn(II) loading rate (45.3 g m−3 day−1) than other reference systems, such as aerobic wetland coupled with algal mats and anoxic limestone drains. The optimum conditions were found to be a CMDS loading of 280 g L−1 and a flow rate of 8 L day−1, and the necessary quantity of CMDS was 91.3 g L−1 day−1, as the replacement cycle of CMDS was determined to be 70 days.