During managed aquifer recharge (MAR) operations, the water chemistry change induced by recharged water can significantly affect both arsenic mobilization from arsenic-containing pyrites and subsequent secondary mineral precipitation. This bench-scale study examined the arsenic mobilization kinetics from arsenopyrite (FeAsS) at MAR relevant conditions in the presence of three model DOM: Suwannee River natural organic matter (SRNOM), Suwannee River humic acid (SRHA), and Suwannee River fulvic acid (SRFA). DOM was found to decrease arsenic mobility during the initial time period (&lt;6 hours) by inhibiting oxidative dissolution, but in the long term (~7 days), it increased arsenic mobility by limiting the formation of secondary precipitation. Among three DOM systems, the SRFA system exhibited the smallest secondary precipitate particles and the slowest crystallization and phase transformation of iron(III) (hydr)oxides. <i>In situ </i>grazing-incidence small angle X-ray scattering (GISAXS) measurements revealed that the initial iron(III) (hydr)oxide nucleation size was decreased in the presence of DOM. These new observations will be aid in tracking arsenic's fate during MAR, and they have implications for other geochemical systems where DOM, arsenic, and iron(III) (hydr)oxide interact.

Dissolved organic matter affects arsenopyrite dissolution and secondary iron(III) (hydr)oxides formation

2019 Fall National Meeting

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