Potential generation and consumption of carbon dioxide during treatment of mine drainages in South Korea

Mine drainage often acts as a source of CO₂-emissions due to pyrite oxidation and the associated production of H⁺, which promotes the dissolution of carbonate minerals. While the treatment of mine drainage with hydrated lime is a common practice to increase pH, the production of lime generates a considerable amount of CO₂. In this study, direct CO₂ emissions from mine drainages and indirect CO₂ emissions from the potential consumption of hydrated lime were modeled using PHREEQ-N-AMDTreat based on chemical compositions and flow rates at most mine drainage sites (n = 395) across South Korea. The total potential CO₂ emissions from the mine drainages were estimated at 481 t yr^-1, with 95 % originating from coal mines. Mine drainages with lower pH and/or higher alkalinity generally exhibited higher CO₂ emissions. In contrast, the potential consumption of hydrated lime to treat all sampled mine drainages could generate 2230 t CO₂ yr^-1, which was >12 times the CO₂ degassed from the drainages, assuming atmospheric equilibrium under surface conditions. Therefore, when considering CO₂ emissions, passive treatment methods are substantially more advantageous than (semi-)active treatment methods using hydrated lime. The estimated CO₂ emissions from most mine drainages were <13 % of the indirect CO₂ emissions attributed to hydrated lime usage. Since the ratio (13 %) is lower than the reported reduction of hydrated lime consumption (22 %-50 %) achieved through pre-aeration in treatment processes, implementing pre-aeration is a preferable approach for most mine drainages from the perspective of CO₂ emission reduction.