A natural attenuation of arsenic in drainage from an abandoned arsenic mine dump

摘要: Abstract At the abandoned As mine in Nishinomaki, Japan, discharged water from mining and waste dump area is acidic rich As. However, concentration drainage has been decreased to below maximum contaminant level (0.01 mg/l for drinking water, Japan) without any artificial treatments before mixing with a tributary populated areas. This implies that naturally attenuated. To elucidate reaction mechanisms of natural attenuation, analysis quality characterization precipitates stream floor were performed by measuring pH, ORP electric conductivity on-site, as well X-ray diffraction, ICP-mass spectrometry ion-chromatography. Selective extractions mineral alteration experiments also conducted estimate distribution constituent phases understand stability As-bearing phases, respectively. The contamination resulted oxidation sulfide minerals rocks, i.e., pyrite realgar subsequent release Fe, SO4, As(V) proton. released Fe(II) transformed Fe(III) bacterial oxidation; schwertmannite then formed immediately. While concentrations lowered nearly background downstream, those ochreous up several tens mg/g. was effectively removed had Although metastable respect goethite, show transformation goethite may be retarded presence absorbed structure. Therefore, attenuation retention are expected maintained long term.