Hg(II) reduction by siderite (FeCO3)

In groundwater, chemical reactions of Hg(II) with mineral surfaces play an important role in determining the concentration of mercury that is mobile and bioavailable. In this study, we investigated Hg(II) reduction by the ferrous carbonate mineral, siderite (FeCO3), to better understand reductive transformation of mercury in anoxic carbonate-bearing waters. Kinetic experiments and X-ray adsorption spectroscopy (XAS) were conducted to examine the rate and mechanism of Hg(II) reaction with siderite. Hg(II) was reacted with synthesized siderite mineral at various concentrations and the subsequently formed Hg(0) was measured to assess the extent of mercury reduction by siderite. Our experimental data showed that Hg(II) reduction by siderite resulted in the loss of Hg when reacted with siderite mineral suspensions concurrent to formation of gaseous Hg(0). Hg(II) reduction occurred within minutes and reaction rates increased with increasing siderite surface area. XAS analysis confirmed that Hg(II) was reduced to Hg(0) and revealed that reduced mercury was sorbed to siderite surfaces suggesting that electron transfer reactions occur at siderite/water interface. The results of our study suggest that Hg(II) reduction by siderite is a kinetically favorable pathway for the mercury mobilization in ferruginous carbonate-bearing waters.