Geochemical characteristics of coal mine discharge vis-a-vis behavior of rare earth elements at Jaintia Hills coalfield, northeastern India

摘要

Geochemical characteristics of dissolved metals including the rare earth elements (REEs) in acid mine drainage (AMD) from Jaintia Hills coalfield, Meghalaya were studied. The mine drainage is characterized by low pH with high concentrations of Fe, Al, Mn, Ni, Pb and SO4~(2-) and REEs. The average total REE concentration in AMD is 714.7 μg/L, which is much higher in comparison to Sitai coalmine drainage. Mine drainage and most of the stream waters from Jaintia coalfield showed a middle REE-enriched pattern when normalizing against North American Shale Composite (NASC). Speciation calculation revealed that Fe~(2+) is the predominant free cation whereas Fe~(3+) and Al~(3+) prevailed as their sulfate complexes. Further, in REE species, REE-sulfate complex (LnSO4~+) accounts for >62%, while free metal (Ln~(3+)) accounts for 24% to 40%. REE pattern indicates that streams are highly impacted by the AMD. Geochemical modeling indicated the supersaturation of various Fe or Al bearing secondary minerals, which possibly control the mobility of metals and REEs.