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. 2018 Aug 29;8(1):13041.
doi: 10.1038/s41598-018-31335-3.

Nanospectroscopy Captures Nanoscale Compositional Zonation in Barite Solid Solutions

Florence T Ling  1 , Heather A Hunter  1 , Jeffrey P Fitts  1 , Catherine A Peters  2 , Alvin S Acerbo  3   4 , Xiaojing Huang  4 , Hanfei Yan  4 , Evgeny Nazaretski  4 , Yong S Chu  4
Affiliations

Nanospectroscopy Captures Nanoscale Compositional Zonation in Barite Solid Solutions

Florence T Ling et al. Sci Rep. .

Abstract

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 (BaSO4) particles precipitated from aqueous solution, in which Sr2+ cations as well as HAsO42- anions were co-precipitated into (Ba,Sr)SO4 or Ba(SO4,HAsO4) 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.

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Conflict of interest statement

The authors declare no competing interests.

Figures

Figure 1
Figure 1
The fractional substitution maps for selected particles from the (Ba,Sr)SO4 experiments, at (a) 1.0 M NaCl, or (b) no additional NaCl. The fractional substitutional maps for the Ba(SO4,HAsO4) experiments, at (c) 1.5 M NaCl, or (d) no additional NaCl. Vectors are drawn for crystal growth directions towards the (100) or (210) surfaces, although morphology and crystal planes could not be determined for the particle displayed in (b).
Figure 2
Figure 2
SEM images of particles displayed in Fig. (a) 1a and (b) 1b taken on a Quanta 200 FE-ESEM, and of (c) 1d, taken on a JEOL JCM-6000 NeoScope.
Figure 3
Figure 3
For a selected Ba(SO4,HAsO4) particle, (a) an SEM image, (b) the phase contrast image, (c) the Ba Lα and (d) the As Kα maps in counts per second (cps) normalized to the ion chamber (I0) reading.
Figure 4
Figure 4
For a selected (Ba,Sr)SO4 particle, maps of emission intensities for (a) Ba Lα, (b) Sr Kα, (c) Cl Kα in counts per second (cps) normalized to ion chamber (I0) reading. Also shown are (d) the SEM image, and (e) the calculated Ba fractional substitution.
Figure 5
Figure 5
Profile plots of the fractional substitution of (a) Sr2+ in a selected particle from the (Ba,Sr)SO4 experiments, and (b) HAsO42− in a selected particle from the Ba(SO4,HAsO4) experiments along the transects corresponding to crystal growth directions indicated in the fractional substitution maps on the right for particles from experiments at high salinities. The growth directions for experiments at low salinity are indicated in Fig. 1b,d.
See this image and copyright information in PMC

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