(Ca,Cd,Zn)CO3 nano-XCT images and 3D elemental maps

Description

This dataset contains synchrotron X-ray computed tomography (XCT) images of mixed-metal carbonate samples, which were coprecipitated with calcium (Ca), cadmium (Cd) and zinc (Zn). The samples were scanned at multiple photon energies at the transmission X-ray microscope (TXM) beamline 32-ID-C of the Advanced Photon Source (APS) at Argonne National Laboratory. The voxel size for every dataset is 20 × 20 × 20 nm3. Specifically, (Ca,Cd)CO3 solid solution and (Ca,Cd,Zn)CO3 solid solution samples were scanned. The samples were experimentally synthesized from aqueous solutions that were supersaturated with respect to all carbonate mineral endmembers: calcite, otavite, and smithsonite. The aqueous concentrations were chosen due to their environmental relevance. These results provide insights about trace element uptake in carbonate host minerals in contaminated environments. The voxel array for the selected (Ca,Cd)CO3 particle was 1024×1024×786. The voxel array for the selected (Ca,Cd,Zn)CO3 particle scanned at 8.000 keV was 2048×2048×1516 and when scanned at 9.675 keV the voxel array was 1224×1224×1316. Additionally, we uploaded the voxel-registered data of the (Ca,Cd,Zn)CO3 particle, which is the end result of spatially registering the voxels in the scans at 8.000 keV and 9.675 keV . These two photon energies were chosen to maximize the X-ray attenuation contrast of Zn. This contrast was necessary for the quantitative analysis of (Ca,Cd,Zn)CO3. This dataset also contains the elemental maps, which are quantitative maps of the chemical compositions of (Ca,Cd)CO3 and (Ca,Cd,Zn)CO3. The elemental maps were generated using LABQ3 (Yi et al., submitted) along a composition continuum, a method fundamentally different from conventional XCT analyses based on segmentation. Analyses revealed rich nano-scale compositional heterogeneity within individual particles. A mixture of calcium and cadmium carbonate revealed an overall composition of (Ca0.78,Cd0.22)CO3, with some voxels containing nearly pure CdCO3. The addition of zinc led to an overall composition of 33% Ca, 28% Cd, 39% Zn, with a nearly pure CaCO3 core and compositional zonation through the rim.