Managed aquifer recharge (MAR) is a widely applied engineering method to combat problems caused by groundwater over-drafting. During MAR operation, the injection of reclaimed water can lead to unfavorable soil−water interactions, causing local minerals to release toxic metalloids, such as arsenic, and forming secondary minerals, such as iron(III) (hydr)oxides. To combat these challenges, it is important to understand the effects of the injected water’s chemistry on arsenic mobilization and secondary mineral precipitation during MAR. In this bench-scale study, the effects of phosphate, silicate, and bicarbonate oxyanions on arsenic mobilization and on secondary mineral precipitation from arsenopyrite (FeAsS) were studied for 7-day at conditions relevant to MAR. Each oxyanion system was tested separately. Phosphate promoted arsenic mobility over a short reaction period (&lt; 1 day) but inhibited arsenic mobility in the long term (&gt; 1 day). During the entire 7-day reaction period, silicate increased arsenic mobility, while bicarbonate inhibited arsenic mobility. In addition, the extent, size, and phases of secondary mineral precipitation varied among three oxyanion systems, further affecting arsenic mobilization. Specifically, in the presence of phosphate, nucleation of phosphosiderite (FePO<sub>4</sub>) promoted the dissolution of FeAsS. In all three oxyanion systems, heterogeneous nucleation of iron oxides and their phase transformation formed hematite and maghemite. These new observations can help us to better understand the fate and transport of arsenic during MAR, and provide useful insights into water chemistry control and pretreatment requirements for MAR source water.

Effects of oxyanions on arsenic mobilization from arsenopyrite during managed aquifer recharge

255th National Meeting (2018)

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