October 20, 2017
Incorporation of Arsenic into Magnetite Reduces Arsenic Mobility in Water
Toxic arsenic (As) adsorbs to the iron (Fe) mineral magnetite and evolves into a less-mobile, incorporated form.
The precipitation of magnetite also removed dissolved Arsenic(V) and provided a stable sink for this water contaminant. Synchrotron X-ray spectroscopy techniques showed that As (V) atoms were incorporated into the magnetite structure, and that As(V) sorbed to preformed magnetite became increasingly incorporated over time and thus resistant to remobilization.
Exposure to As in groundwater affects millions of people around the globe. The results of this study increase understanding of how iron minerals affect As mobility in natural systems and provide the molecular-level insight needed for the development of iron oxide–based As removal technologies. The study was highlighted on the cover of the October 2017 issue of Environmental Science: Processes and Impacts.
The use of As-contaminated water for irrigation or as a drinking water source is threatening human health in many regions of the world. Iron is the element that most strongly correlates with As in sediments, and As mobilization is frequently linked with the desorption/dissolution of As from iron oxides. Technologies for As removal from drinking water also rely on the sequestration of As with Fe oxides (e.g., using electrocoagulation or zero-valent iron filters. A team of scientists from Argonne National Laboratory, the University of Iowa, Newcastle University, and the Bulgarian Academy of Sciences elucidated the molecular-level interactions between dissolved As(V) and magnetite, a common product of iron corrosion or dissimilatory iron reduction. Using synchrotron X-ray techniques (XANES and EXAFS spectroscopy), the team found that co-precipitation of As(V) and magnetite results in incorporation of the As(V) ions into the structure of magnetite, whereas reactions of As(V) with preformed magnetite show a transformation from initially adsorbed As(V) to incorporated As(V). Selective chemical extractions show that once As is incorporated into magnetite it could not be remobilized, neither in the absence nor in the presence of aqueous Fe(II), suggesting that magnetite is a stable sink for As(V).
Argonne National Laboratory
U.S. Department of Energy, Biological and Environmental Research (SC-33)
Environmental System Science
This research is part of the Subsurface Science Scientific Focus Area at Argonne National Laboratory (ANL), which is supported by the Subsurface Biogeochemical Research Program of the Office of Biological and Environmental Research, within the U.S. Department of Energy Office of Science. Use of the Electron Microscopy Center and the Advanced Photon Source (APS) at ANL is supported by the Office of Basic Energy Sciences within the DOE Office of Science. MRCAT/EnviroCAT operations at APS are supported by DOE and the MRCAT/EnviroCAT member institutions. All work at ANL was under Contract DE-AC02-06CH11357.
Huhmann, B. L., A. Neumann, M. I. Boyanov, and K. M. Kemner, et al. "Emerging investigator series: As(V) in magnetite: incorporation and redistribution". Environmental Science: Processes & Impacts 19 (10), 1208–1219 (2017). http://dx.doi.org/10.1039/c7em00237h.