During groundwater discharge into the river,Fe2+and As3+in anoxic groundwater are brought into the oxygen-containing interaction zone. This study explores the co-migration and transformation mechanism of Fe2+and As3+with groundwater in the natural sediment medium.The migration and transformation rules of Fe2+and As3+during groundwater discharge into river water and the transformation rate of Fe2+and As3+to solid phase (solidification) in different regions of the interaction zone are studied by laboratory column experiment and batch experiment.The results show that the sediment strongly adsorbs Fe2+and As3+,and As3+accelerates the migration of Fe2+. The chemical oxidation and precipitation of Fe2+occur,and Fe-As bounding minerals are formed when it flows through the interaction zone.The solidification rate of Fe2+and As3+is accelerated from the area far from the river to that near the river. In the whole interaction zone,Fe2+significantly promotes the solidification of As3+,while As3+slightly inhibits the solidification of Fe2+near the river bank.In short,during groundwater discharge into river water,the synergistic chemical oxidation and adsorption fixation of Fe2+and As3+in groundwater occur at different rates in different regions of the interaction zone,which seriously hinders their migration to river water.
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