Assessment of mechanisms and efficiencies for Mn decrease at unit processes in passive treatment facilities for mine...

In passive treatment facilities, a limestone reaction and oxidation alone are generally ineffective in treating Mn, but decreases in Mn concentration are observed. Predicting Mn decrease efficiency and assessing the mechanisms underlying Mn treatment in passive treatment facilities are important steps in calculating the area required for conventional Mn treatment or in deciding whether the addition of limestone beds, slag leach beds, slag reactors, or the Pyrolusite process is required. In this study, data from passive treatment facilities in South Korea and batch limestone experiments revealed that Mn coprecipitation and adsorption by Fe were unlikely to occur. Principal factors for decrease in Mn concentrations were found to be water depth and the Fe(II) concentration. These findings may enhance our understanding of the mechanisms by which Mn is effectively decreased in aerobic wetlands. The decrease rates of Mn concentration for each unit process in conventional passive treatment facilities were calculated, which were 0.03, 0.31, and 0.93 mg L^-1 day^-1 on average, respectively, in oxidation ponds, successive alkalinity producing systems (SAPS), and aerobic wetlands. These differences in Mn decrease efficiencies may be taken into account when designing or renovating passive treatment facilities.