INVESTIGATION OF ARSENIC RELEASE FROM SEDIMENT MINERALS TO WATER PHASES -MOTIVATION FOR ARSENIC MITIGATION TECHNOLOGY

Severe and widespread contamination by arsenic in groundwater and drinking water has been recently revealed in rural and sub-urban ania of Vietnamese capital of Hanoi with similar magnitude observed in Bangladesh and West Bengal, India.Tlus fact has prompted the need to investigate the possible mechanisms for such widespread contamination and develop suitable tecluuques for lowering arsenic concentrations in supplied water.In the present study, laboratory-scale experiments were perfonned to assess the possible release of arseluc from solid phase into water phase under both anaerobic and aerobic conditions.Various chemical equilibrations govenling the speciation of different ions in water phase and alluvial sediment are discussed.Under anaerobic conditions, the release of arsenic seemed to be closely related to the content of Mn02 in sediments, the reduction ofFe(III) to Fe(II) and the formed sulfur content.Elevated Mn02 content may inhibit the release of arsenic to groundwater.The reduction of arsenic concentrations in water phases could be due to the formation of Fe2AsS or AsH 3 .In aerobic conditions, the hydrothelmal oxidation process was proposed as a plausible mechanism of release of arsenic from arsenic-rich mineral surfaces to water phases.In acidic conditions, arsenic concentrations increased due to the more effective release from mineral surfaces, Under neutral medium (PH :::: 7), the arsenic releasing was less efficacious, which could be due to the co-precipitation onto ferric hydroxide.The possible mechanisms suggested in this study may be usefhl to explain the elevated contamination of arsenic in surface waters of upstream rivers of mountain areas in northem Vietnam and in underground water of Rivers delta, and critical for moving to tlle next stage in developing suitable teclmiques for lowering arsenic concentrations in groundwater and drinking water in Vietnam.