Assessing Pilot-Scale Treatment Facilities with Steel Slag-Limestone Reactors to Remove Mn from Mine Drainage.

Pilot-scale mine water treatment facilities were operated for over four years at the Ilwol mine, South Korea. A steel slag-limestone reactor (referred to as the slag reactor) was tested and a successive alkalinity producing system (SAPS) and a SAPS incorporating slag from a basic oxygen steelmaking furnace were compared. The SAPS decreased Mn from 23.3 to 7.4 mg L−1 on average because the alkalinity generated led to saturation with rhodochrosite. Adding a slag reactor removed Mn down to levels of 0.002–1.8 mg L−1 from influent Mn as high as 17.1 mg L−1 with a residence time of 5–25 h. Mn-containing carbonates and oxides were precipitated, which was supported by the geochemical modelling and observed with scanning electron microscopy with energy dispersive spectroscopy. The increased alkalinity in the SAPS before the slag reactor helped remove Mn at a pH range of 8.0–8.3. Mn removal rates and Mn-standardized Mn removal rates in the slag reactor were 0.76 mg L−1 h−1 and 0.105 h−1 in average, respectively. The passive treatment of Mn using an Fe-pretreatment and alkalinity-generation system, a slag-limestone reactor, and a wetland rather than a SAPS including slag, an oxidation-settling pond, and a wetland is suggested to consistently meet the effluent standards for Mn and pH. [ABSTRACT FROM AUTHOR]