Characteristics and treatment technologies for acid mine drainage from abandoned coal mines in major coal-producing countries

Major coal-producing countries have all experienced AMD pollution (acid mine drainage) which constitutes a global environmental challenge from the mining industry. Based on a constructed conceptual model for the origin of AMD and water quality evolution pattern under whole life cycles of coal mining, the occurrence characteristics of coal resources in major coal-producing countries are reviewed, and the AMD characteristics and key influencing factors are clarified. The results show that the characteristics of AMD in coal mines are influenced by coal-forming environments, water-rock interactions and climatic conditions, among which the sulfur in coal is a primary influencing factor. Coals in the Carboniferous to Permian coal-bearing strata of the Late Paleozoic Era in southern China and eastern United States are developed in alternating marine and terrestrial environments, containing high sulfur in coals ( > 3%), and the AMD is highly acidic with elevated sulfate and metallic concentrations. Whereas the coal-bearing strata developed in the deltaic plain environments, such as those found in parts of China and in western USA, are characterized with medium sulfur in the coals and produce weakly acidic or alkaline AMD with relatively elevated sulfate concentrations; In the United Kingdom, the Carboniferous low-sulfur coal primarily produce weakly acidic or alkaline AMD, however, some areas may also experience high salinity due to seawater intrusion in the underground voids; Australia and India have the Permian fluvial delta environments with the coal-bearing strata that contain low sulfur content ( < 1%) in the coals. the AMD in these areas is typically neutral or weakly alkaline with low concentrations of sulfate and iron; In northeastern India, acidic AMD is produced from the Cenozoic high-sulfur coal. To address the AMD with different characteristics, some low-cost and sustainable in-situ treatment multi-technologies are proposed for AMD treatment in abandoned coal mines.