Effects of mining activities on Fe, Mn, and Zn in mine water: insights from experimental of water-coal/rock interaction

Mining activities affect the metal concentrations in mine water (MW). However, mechanism of metals enrichment in MW under mining activities is not well understood. This study investigates the relationships between Fe, Mn, and Zn concentrations in MW and its recharge sources, and the geochemical composition of surrounding rock and coal. Water-coal/rock interaction experiments were conducted to study the mechanisms of metal dissolution, considering both the metal occurrence forms and types of dissolved organic matter (DOM). Results indicate that coal mining significantly disturbs the original geological structure and environment, facilitating groundwater flow from Aquifer Ⅲ into mining areas. Prolonged interaction between groundwater and fractured coal/rock significantly enhanced Fe, Mn, and Zn leaching. Fe and Zn were elevated 9.88-fold and 3.44-fold, respectively, compared to Aquifer Ⅲ (0.93 and 1.08 mg/L), while Mn changed slightly compared with Aquifer Ⅲ (0.17 mg/L). Fe exhibited the highest leachability, primarily originating from exchangeable and carbonate bounded forms during water-coal/rock interaction. Concurrently, DOM dissolution from coal released humic acids, promoting desorption of metals. Metal release during water-coal interaction follows a peak function ( R 2 > 0.83). While metal release during water-rock interaction fits with an exponential function ( R 2 > 0.94). Although metal release patterns differ between water-coal and water-rock interaction, both processes collectively govern metal concentration in MW. This study demonstrates metal occurrence forms and DOM participation influence metal enrichment in MW during water-coal/rock interaction following coal mining disturbance.