Metal (Fe, Cu, and As) transformation and association within secondary minerals in neutralized acid mine drainage characterized using X-ray absorption spectroscopy

The formation and transformation of secondary minerals in areas affected by neutralized acid mine drainage (AMD) determine the behavior toxic elements. To better understand binding form elements minerals, we focused on distribution precipitates heavy metals AMD near a typical Cu-polymetallic deposit located central Tibet. Compared to background values, average metal (As, Cu, Co, Mo, Pb, Zn) content is higher sediments close drain. X-ray absorption spectroscopy (XAS) characterization shows Fe suspended particulate matter (SPM) first aggregate as small Fe(III) octahedra clusters then precipitate ferrihydrite along river. XAS results also show by-products neutralization—ferrihydrite sulfate—are primary forms S sediments, respectively. Gypsum retains Cu via structural fixation, surface adsorption, coprecipitation. difference Cu-O coordination number between SPM reveals sulfate coprecipitation gypsum accompanied transporting confirm that act an essential sink for metals, especially As. As(III) mineral sediment outfall dissolved oxidized arsenate downstream, which adsorb and/or As(V)-Fe have potential release with changes water chemistry, may pose threat safety drinking downstream residents. deepen understanding influence (especially ferrihydrite) migration process pollutants system.