Ling Florence T, Hunter Heather A, Fitts Jeffrey P, Peters Catherine A, Acerbo Alvin S, Huang Xiaojing, Yan Hanfei, Nazaretski Evgeny, Chu Yong S
Department of Civil and Environmental Engineering, Princeton University, Princeton, NJ, 08544, USA.
Center for Advanced Radiation Sources (CARS), University of Chicago, Chicago, IL, 60637, USA.
Sci Rep. 2018 Aug 29;8(1):13041. doi: 10.1038/s41598-018-31335-3.
Scientists have long suspected that compositionally zoned particles can form under far-from equilibrium precipitation conditions, but their inferences have been based on bulk solid and solution measurements. We are the first to directly observe nanoscale trace element compositional zonation in <10 µm-sized particles using X-ray fluorescence nanospectroscopy at the Hard X-ray Nanoprobe (HXN) Beamline at National Synchrotron Light Source II (NSLS-II). Through high-resolution images, compositional zonation was observed in barite (BaSO) particles precipitated from aqueous solution, in which Sr cations as well as HAsO anions were co-precipitated into (Ba,Sr)SO or Ba(SO,HAsO) solid solutions. Under high salinity conditions (NaCl ≥ 1.0 M), bands contained ~3.5 to ~5 times more trace element compared to the center of the particle formed in early stages of particle growth. Quantitative analysis of Sr and As fractional substitution allowed us to determine that different crystallographic growth directions incorporated trace elements to different extents. These findings provide supporting evidence that barite solid solutions have great potential for trace element incorporation; this has significant implications for environmental and engineered systems that remove hazardous substances from water.
长期以来，科学家们一直怀疑成分分带颗粒可以在远离平衡沉淀的条件下形成，但他们的推断是基于对块状固体和溶液的测量。我们首次使用美国国家同步辐射光源II（NSLS-II）的硬X射线纳米探针（HXN）光束线的X射线荧光纳米光谱，直接观察了尺寸小于10微米的颗粒中的纳米级微量元素成分分带。通过高分辨率图像，在从水溶液中沉淀出的重晶石（BaSO）颗粒中观察到了成分分带，其中Sr阳离子以及HAsO阴离子共沉淀到（Ba，Sr）SO或Ba（SO，HAsO）固溶体中。在高盐度条件下（NaCl≥1.0M），与颗粒生长早期形成的颗粒中心相比，条带中的微量元素含量多出约3.5至5倍。对Sr和As分数替代的定量分析使我们能够确定不同的晶体生长方向对微量元素的掺入程度不同。这些发现为钡固溶体具有巨大的微量元素掺入潜力提供了支持证据；这对从水中去除有害物质的环境和工程系统具有重要意义。
