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.