Spatiotemporal leaching dynamics and mechanistic insights into heavy metal release from ion-adsorbed rare earth tailings under acid rain conditions

Acid rain not only triggers the release of heavy metals from ion-adsorption rare earth tailings, but also shapes their spatiotemporal distribution, increasing environmental risks. This study investigated the release behavior and spatiotemporal distribution of heavy metals in ion-adsorption rare earth tailings under acid rain conditions using static and column leaching experiments. The analysis indicated that in the tailings of the study area, the concentrations of As, Mn, Pb, Zn, Cd, Cu and Cr reached 35.35、542.68、209.73、178.21、0.82、31.34、82.82 mg⋅kg ⁻1 , respectively, which were several times higher than the background values, indicating that mining activities cause serious pollution. Static leaching experiments identified As, Mn, Pb, and Zn as priority pollutants requiring control. Dynamic column leaching studies revealed that, from the time dimension, the heavy metal release process could be clearly divided into two stages: rapid leaching and slow release; from the spatial dimension, it exhibited a "low at the bottom, high at the top" vertical gradient pattern, with the leachate concentrations of As, Mn, Pb, and Zn significantly exceeding environmental limits. The DoseResp model accurately fitted all heavy metal leaching processes. Key factors controlling heavy metal migration included chemical speciation, rainfall pH, SO 4 2 − concentration, ammonia nitrogen, and mineral properties, with acid-extractable fractions showing preferential release during leaching. The research findings provide a scientific basis for ecological restoration of ion-adsorption rare earth mines and source control of heavy metal pollution in tailings. • Leaching reveals As, Mn, Pb, and Zn as key pollutants in rare earth tailings. • Heavy metal release occurs in two stages: fast leach then slow diffusion. • Leachate shows a bottom-low, top-high profile, exceeding environmental limits. • DoseResp model fits kinetics well; Mn and Zn exhibit fastest diffusion rates. • pH and mineral traits are key factors driving heavy metal migration behavior.