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

本文研究了Cr6+、Cu2+和Ni2+在赤铁矿(α-Fe2O3)中结构掺杂的物理化学机理。赤铁矿是赤泥的主要成分，赤泥是铝生产中产生的一种有毒废物。赤泥通常含有高浓度的铬、铜和镍，它们主要与赤铁矿相伴生。由于这三种金属都具有很高的经济重要性，赤泥可能是未来回收作业的潜在原材料。为了最有效地从赤泥中提取铬、铜和镍，有关主要载体相和准确的结构结合机理的信息是至关重要的。对于铬，只有Cr3+的数据，由于赤铁矿(Fe2O3)和硅灰石(Cr2O3)的结构相似，Cr3+占据了Fe3+的位置，但Cr6+的结构结合到目前为止还没有得到研究。Cu2+和Ni2+的结构结合受到以前几个研究的制约，没有确凿的和经验支持的模型。因此，本项目有三个主要目标：(1)确定合成赤铁矿样品中Cr6+、Cu2+和Ni2+的结构结合机制；(Ii)将在实验室条件下形成的人造赤铁矿的结合机制转移到赤泥蓄水池的天然赤铁矿中；(Iii)估计德国(活跃的和废弃的)赤泥蓄水池未来回收利用的潜力。拟议的研究将包括含Cr6+、Cu2+和Ni2+的赤铁矿的合成、化学和晶体表征，以及天然和合成赤铁矿中感兴趣的金属周围的短程有序性的调查。所采用的方法包括粉末X射线衍射法、电感耦合等离子体质谱(ICPMS)、质谱仪耦合气体发射系统(DEGA)、透射电子显微镜(TEM)和X射线吸收光谱(XAS)、X射线近边吸收光谱(XANES)和扩展X射线吸收精细结构光谱(EXAFS)。本研究将大大提高我们对赤铁矿非均相取代机理的认识，为赤泥作为潜在资源的研究奠定基础。

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.