Abstract:
Acid coal mine drainage has emerged as one of the most challenging environmental problems in the coal industry because of its large output, wide pollution range, long duration, and unstable water quality and quantity. This paper summarizes and analyzes the pollution situation, causes, and basic characteristics of acid coal mine drainage. To date, leaching pollution is caused by underground goaf water and coal gangue accumulation, which are the two main sources of acid coal mine drainage. Containing a large amount of soluble iron, manganese ions, and suspended solids, acid coal mine drainage has a low pH, unstable effluent quality and quantity, wide pollution range, and long duration. Acid coal mine drainage production differs between large coal mine factories and small and medium coal mine factories. A large amount of water in underground goaf accumulates after the closure of small and medium coal mine factories, resulting in the oxidation of coal and producing acid coal mine drainage. Large coal mines have not been closed mainly because of the large accumulation of coal gangue, producing leaching pollution and discharging a large amount of acid coal mine drainage. Given the difference in acid coal mine drainage production between the two types of mines, they require different treatment methods. To control acid coal mine drainage pollution, closed coal mines in China mainly apply terminal treatment technologies, such as common chemical neutralization, SRB microbial, wetland system construction, and biochar adsorption technologies, which have been developed and utilized in recent years. However, owing to the continuous pollution of water sources, the treatment of acid coal mine drainage pollution in large coal mine plants depends only on terminal treatment, which is time-consuming, costly, and inadequate treatment effect. Hence, increasing source control and path interception technologies is necessary. Source control technologies, such as sterilization, coverage, passivation, and carrier-microencapsulation technologies, have been developed, and path control technologies, such as the roadway closed filling technology, have been used, but they are not yet mature. This paper summarizes existing technologies for acid coal mine drainage treatment from three aspects: source treatment, path blocking, and end treatment. These technologies are based on different processes that produce acid drainage in large coal mines and small and medium coal mines. The path management mode requires the study of the sources, channels, and propagation paths of pollutants, given that this mode mitigates goaf and groundwater pollution by blocking sources and propagation paths, controlling pollution areas, and cutting off the connection between water layers. In view of the challenges in acid utilization and heavy metal recovery in the current acid coal mine drainage treatment, this paper proposes the following concepts: “comprehensive utilization of resources” to recover valuable substances, “treating waste with waste” acid–base neutralization, and overall comprehensive treatment.