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

在这里，我们建议调查的物理化学机制的Cr 6+，Cu 2+，和Ni 2+的结构纳入赤铁矿（α-Fe 2 O3）。赤铁矿是铝生产过程中产生的一种有毒废料--红泥的主要成分。红泥通常含有高浓度的Cr、Cu和Ni，其主要与赤铁矿相相关联。由于这三种金属都具有很高的经济重要性，因此红泥可能是未来回收作业的潜在原材料。为了从赤泥中最有效地提取Cr、Cu和Ni，关于主要载体相和精确的结构并入机制的信息是至关重要的。对于铬，只有Cr 3+的数据是可用的，它占据了Fe 3+的位置，由于结构相似的赤铁矿（Fe 2 O 3）和铁铬铅矿（Cr 2 O 3），但尚未研究到目前为止，Cr 6+的结构掺入。由于Cu ~（2+）和Ni ~（2+）的结构结合受到以往研究的限制，没有结论性的经验支持模型，因此本项目有三个主要目标：（i）确定合成赤铁矿样品中Cr ~（6+）、Cu ~（2+）和Ni ~（2+）的结构结合机制;（ii）从在实验室条件下形成的合成赤铁矿转移所获得的结合机制，（iii）对德国赤泥库潜力的评估拟议的研究将包括含Cr 6+、Cu 2+和Ni 2+的赤铁矿的合成，化学和晶体学表征，以及研究天然和合成赤铁矿中感兴趣的金属周围的短程有序。使用的方法包括粉末X射线衍射、电感耦合等离子体质谱（ICP-MS）、质谱仪耦合气体发射系统（DEGAS）、透射电子显微镜（TEM）和X射线吸收光谱（XAS），X射线吸收近边光谱（XANES）和扩展X射线吸收精细结构光谱（EXAFS）该研究将有助于加深对赤铁矿非均相取代机理的认识，为今后赤泥资源化研究奠定基础。

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.