The experimental replacement of ilmenite by rutile in HCl solutions
The experimental replacement of ilmenite by rutile in HCl solutions
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DOI：
10.1180/minmag.2010.074.4.633
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发表时间：
2010-08-01
影响因子：
2.7
通讯作者：
Putnis, C. V.
中科院分区：
文献类型：
--
作者：
Janssen, A.;Putnis, A.;Putnis, C. V.
为了确定钛铁矿酸浸最终形成金红石的机理，我们在高压釜中进行了钛铁矿在150 ℃盐酸溶液中的蚀变实验研究。用X射线衍射、扫描电子显微镜、电子探针和拉曼光谱对产物进行了表征。在一些实验中，溶液最初富含（18）O，并且同位素在蚀变产物中的分布由拉曼光谱中阳离子-氧伸缩带的频移绘制。蚀变开始于原始钛铁矿晶体表面，并且还沿着由反应产生的钛铁矿中的裂缝的复杂分支网络发生。元素分布图和化学分析的反应产物内的裂缝显示显着的贫化铁和锰和相对富集的钛。然而，化学分析不对应于任何化学计量组成，并且可能代表TiO（2）和Fe（2）O（3）的混合物。断裂可能是由与钛铁矿溶解和产物相（包括金红石）从界面溶液中沿沿着向内移动的溶解-再沉淀前沿同时再沉淀相关的体积变化驱动的。拉曼光谱表明，在再结晶过程中，（18）O进入了金红石结构。在整个蚀变过程中，钛铁矿的原始形态被保留，尽管产品是高度多孔的。金红石继承了来自母钛铁矿的晶体学信息，从而产生了三晶孪晶金红石显微结构。结果表明，钛铁矿被金红石直接置换，没有中间反应产物生成。该反应描述的界面耦合溶解-沉淀机制。
To determine the mechanism of acid-leaching of ilmenite to ultimately forming rutile, we have carried out an experimental study of ilmenite alteration in autoclaves at 150 degrees C in HCl solutions. The resulting products were studied by X-ray diffraction, scanning electron microscopy, electron microprobe and Raman spectroscopy. In some experiments the solution was initially enriched in (18)O and the distribution of the isotope in the alteration products mapped from the frequency shift of cation-oxygen stretching bands in the Raman spectra. The alteration begins at the original ilmenite crystal surface and has also taken place along an intricate branching network of fractures in the ilmenite, generated by the reaction. Element-distribution maps and chemical analyses of the reaction product within the fractures show marked depletion in Fe and Mn and a relative enrichment of Ti. Chemical analyses however, do not correspond to any stoichiometric composition, and may represent mixtures of TiO(2) and Fe(2)O(3). The fracturing is possibly driven by volume changes associated with dissolution of ilmenite and simultaneous reprecipitation of the product phases (including rutile) from an interfacial solution along an inward moving dissolution-reprecipitation front. Raman spectroscopy shows that the (18)O is incorporated in the rutile structure during the recrystallization. Throughout the alteration process, the original morphology of the ilmenite is preserved although the product is highly porous. The rutile inherits crystallographic information from the parent ilmenite, resulting in a triply-twinned rutile microstructure. The results indicate that the ilmenite is replaced directly by rutile without the formation of any intermediate reaction products. The reaction is described in terms of an interface-coupled dissolution-precipitation mechanism.