Reductive transformation of oxyanion-containing jarosite by iron-reducing bacteria: Effects of mineral precipitation on the mobility of potentially toxic elements

Abstract

Jarosite can co-precipitate with hazardous oxyanions and reduce their concentration. However, the redox conditions significantly affect the mobility of these elements. We investigated the mineral phase change and mobility changes of oxyanions in jarosite containing different mole percentages of arsenate (AsO₄^3-), chromate (CrO₄^2-), molybdate (MoO₄^2-), selenate (SeO₄^2-), and selenite (SeO₃^2-) during reduction by Shewanella putrefaciens. The mineralogical and chemical changes were characterized using X-ray diffraction (XRD), scanning and transmission electron microscopy (SEM/TEM), and inductively coupled plasma-optical emission spectroscopy (ICP-OES). The mole percentage and oxyanion species significantly affected the mineral transformation and mobility changes during the reduction process. The 2-mole percentage oxyanions generally showed faster mineral phase transformation than 10-mole percent, likely due to the inhibition of reductive dissolution at high oxyanion concentrations and the toxicity of CrO₄²⁻. The reduction process greatly enhanced the iron concentration, mineral transformation, and the mobility of these elements compared to the abiotic controls. Goethite was precipitated first, followed by siderite. This process eventually reduced the dissolved iron concentration and led to a decrease in dissolved oxyanions due to their adsorption onto the surfaces of these newly formed minerals. Extra mineral precipitation, parasymplesite for AsO₄-jarosite, selenium particles for SeO₄- and SeO₃-jarosite, and iron selenide for 10-mole percent SeO₃-jarosite, contributed to an additional decrease in these two elements in solution. Our results show that the reduction process by bacteria plays an important role in the cycle of iron and mobility changes of oxyanions.