Engineered mineralogical interfaces as radionuclide repositories.

Effective capture of fugitive actinides and daughter radionuclides constitutes a major remediation challenge at legacy or nuclear accident sites globally. The ability of double-layered, anionic clay minerals known as hydrotalcites (HTC) to contemporaneously sequester a range of contaminants from solution offers a unique remedy. However, HTC do not provide a robust repository for actinide isolation over the long term. In this study, we formed HTC by in-situ precipitation in a barren lixiviant from a uranium mine and thermally transformed the resulting radionuclide-laden, nanoscale HTC. Atomic-scale forensic examination of the amorphized/recrystallised product reveals segregation of U to nanometre-wide mineral interfaces and the local formation of interface-hosted mineral grains. This U-phase is enriched in rare earth elements, a geochemical analogue of actinides such as Np and Pu, and represents a previously unreported radionuclide interfacial segregation. U-rich phases associated with the mineral interfaces record a U concentration factor of ~ 50,000 relative to the original solute demonstrating high extraction and concentration efficiencies. In addition, the co-existing host mineral suite of periclase, spinel-, and olivine-group minerals that equate to a lower mantle, high P-T mineral assemblage have geochemical and geotechnical properties suitable for disposal in a nuclear waste repository. Our results record the efficient sequestering of radionuclides from contaminated water and this novel, broad-spectrum, nanoscale HTC capture and concentration process constitutes a rapid solute decontamination pathway and solids containment option in perpetuity.

Remineralization and fluoride uptake of white spot lesions under dental varnishes.

INTRODUCTION: The aim of this study was to evaluate white spot lesion (WSL) remineralization and fluoride uptake by the application of fluoride varnishes directly onto artificial WSLs in vitro. METHODS: MI varnish containing casein phosphopeptide-amorphous calcium phosphate (CPP-ACP) and 2.26% fluoride and Duraphat varnish containing 2.26% fluoride (no added calcium) were compared with a placebo varnish (no added calcium or fluoride). Two WSLs were prepared in enamel slabs and varnish applied to cover one of the two lesions. Each slab was immersed in artificial saliva for 14 days at 37°C. Mineral content was determined using transverse microradiography and fluoride uptake using electron probe microanalysis. The data were statistically analysed using a linear mixed model. RESULTS: Both MI and Duraphat varnishes significantly remineralized the covered and uncovered WSLs when compared with the placebo varnish (P < 0.001). The WSLs covered with varnish showed greater remineralization than those uncovered. MI varnish produced the highest level of remineralization and significantly greater fluoride uptake (0.44 ± 0.08 wt%) compared with Duraphat (0.24 ± 0.03 wt%) and the placebo varnish (0.06 ± 0.05 wt%). CONCLUSION: Varnish containing fluoride and CPP-ACP was superior to varnish containing fluoride alone in promoting WSL remineralization and fluoride uptake.

Hyperspectral cathodoluminescence imaging and analysis extending from ultraviolet to near infrared.

The measurement of near-infrared (NIR) cathodoluminescence (CL) with sufficient sensitivity to allow full spectral mapping has been investigated through the application of optimized grating spectrometers that allow the ultraviolet (UV), visible, and NIR CL spectra to be measured simultaneously. Two optical spectrometers have been integrated into an electron microprobe, allowing simultaneous collection of hyperspectral CL (UV-NIR), characteristic X-rays, and electron signals. Combined hyperspectral CL spectra collected from two natural apatite (Ca5[PO4]3[OH,F]) samples from Wilberforce (Ontario, Canada) and Durango (Mexico) were qualitatively analyzed to identify the emission centers and then deconvoluted pixel-by-pixel using least-squares fitting to produce a series of ion-resolved CL intensity maps. Preliminary investigation of apatite has shown strong NIR emissions associated primarily with the rare-earth element Nd. Details of growth and alteration were revealed in the NIR that were not discernable with electron-induced X-ray mapping. Intense emission centers from Nd3+ and Sm3+ were observed in the spectra from both apatites, along with minor emissions from other 3+ rare-earth elements. Quantitative electron probe microanalysis was performed on points within the mapped area of the Durango apatite to produce a calibration line relating cathodoluminescent intensity of the fitted peak centered at 1,073 nm (1.156 eV) to the Nd concentration.