Mining activities generate acid mine drainage (AMD), which requires treatment to prevent contamination and acidification of aquatic environments. Active treatment is widely applied because of its high efficiency and operational capacity; however, its substantial energy and chemical demands can lead to high CO 2 emissions. This study establishes detailed and simplified methods for estimating CO 2 emissions from AMD active treatment plants. Unlike existing approaches, the proposed method enables evaluation of carbon transformations among different carbon species throughout the treatment processes, allowing a more comprehensive carbon-flow assessment. CO 2 emissions from four full-scale AMD active-treatment plants in Japan were evaluated, and carbon flows during treatment were analyzed. The results showed that direct and indirect emissions varied among the plants due to differences in neutralizers. On average (except plant D), neutralizer-derived CO 2 accounted for 61% of total emissions, electricity-related emissions for 36%, and other sources for 3%, highlighting the dominant influence of neutralizer selection. Major contributors were the use of CaCO 3 as the neutralizer (through both its reaction with AMD and its calcination-derived Ca(OH) 2 supply) and electricity consumption. Across all plants, part of the inorganic carbon was converted into organic carbon, and plants using Ca(OH) 2 absorbed atmospheric CO 2 during treatment. The error between detailed and simplified estimates was small in CaCO 3 -based systems and larger in Ca(OH) 2 -based systems. • Detailed and simplified CO 2 accounting was developed for acid mine drainage active treatment. • CO 2 emissions from several real AMD treatment plants were evaluated. • Neutralizer was the largest contribution to CO 2 emissions, followed by energy use. • Some CO 2 was absorbed into the acid mine drainage during treatment.
Du et al. (2026) studied this question.