Structural incorporation mechanisms of Cr6+, Cu2+, and Ni2+ in hematite (alpha-Fe2O3)

• Applicant: Dr. Ralph Bolanz
• Subject Area: Mineralogy, Petrology and Geochemistry
• Term: from 2015 to 2019
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 277091282

Here we propose to investigate the physicochemical mechanisms for the structural incorporation of Cr6+, Cu2+, and Ni2+ into hematite (alpha-Fe2O3). Hematite represents a main constituent of red mud, a toxic waste material arising from aluminum production. Red mud contains often high concentrations of Cr, Cu, and Ni, which are predominantly associated with the hematite phase. Since all three metals possess a high economic importance, red mud could be a potential raw material for future recycling operations. For a most efficient extraction procedure of Cr, Cu, and Ni from red mud, information about the main carrier phases and the exact structural incorporation mechanisms are of vital importance. For chromium, only data for Cr3+ is available, which occupies the Fe3+ position due to the structural similarities of hematite (Fe2O3) and eskolaite (Cr2O3), the structural incorporation of Cr6+, however, has not been investigated until now. The structural incorporation of Cu2+ and Ni2+ was subject to several previous studies without conclusive and empirically supported modelsTherefore this project has three main goals (i) identify the structural incorporation mechanisms for Cr6+, Cu2+, and Ni2+ in synthetic hematite samples; (ii) transfer of the acquired incorporation mechanisms from synthetic hematite, formed under laboratory conditions, to natural hematite from red mud impoundments (iii) estimation of the potential of red mud impoundments in Germany (active and abandoned) for future recycling operations.The proposed study will include the synthesis of Cr6+, Cu2+, and Ni2+-bearing hematite, the chemical and crystallographic characterization, as well as the investigation of the short-range order around the metals of interest in natural and synthetic hematite. The methods to be used comprise powder X-ray diffraction, inductively-coupled plasma mass spectrometry (ICP-MS), mass spectrometer-coupled gas emission system (DEGAS), transmission electron microscopy (TEM), and X-ray absorption spectroscopy (XAS), both X-ray absorption near edge spectroscopy (XANES) and extended X-ray absorption fine structure spectroscopy (EXAFS).It is expected that this study will significantly improve our understanding about heterogeneous substitution mechanisms in hematite and establish the foundation for future research on red mud as potential resource.

• DFG Programme: Research Grants
• International Connection: Slovakia
• Cooperation Partner: Privatdozent Dr. Peter Uhlík