RESUMEN
We evaluated the potential of time-resolved laser-induced fluorescence spectroscopy (TRLFS) combined with chemometric methods for fast identification of U(VI)-bearing minerals in a mining context. We analyzed a sample set which was representative of several environmental conditions. The set consisted of 80 uranium-bearing samples related to mining operations, including natural minerals, minerals with uranium sorbed on the surface, and synthetic phases prepared and characterized specifically for this study. The TRLF spectra were processed using the Ward algorithm and the K-nearest neighbors (KNN) method to reveal similarities between samples and to rapidly identify the uranium-bearing phase and the associated mineralogical family. The predictive models were validated on an independent dataset, and then applied to test samples mostly taken from U mill tailings. Identification results were found to be in accordance with the available characterization data from X-ray diffraction (XRD) and scanning electron microscopy-energy dispersive X-ray spectrometry (SEM-EDX). This work shows that TRLFS can be an effective decision-making tool for environmental investigations or geological prospection, considering the large diversity of uranium-bearing mineral phases and their low concentration in environmental samples.
RESUMEN
In this study, synthetic copper substituted hydroxyapatite (Cu-Hap), CuxCa10-x(PO4)6(OH)2 were prepared by co-precipitation method and were used as reactive materials in batch experiments to immobilize uranyl. The limit of incorporation of Cu into a single-phased Cu-Hap reached xCu ≤1.59. The synthetic Cu-Hap samples obtained with various Cu contents were contacted with synthetic uranyl doped solutions and with real mining waters showing various pH and chemical compositions. A fast and strong decrease of the uranium concentration was observed, followed by the establishment of an equilibrium after 1-4 days of contact with the solutions. Examination of the solid phase after uranium uptake was performed using a combination of techniques. Depending on the composition of the solution and the copper content of the Cu-Hap, various mechanisms of uranium removal were observed. Based on the experimental results and geochemical simulations, it appeared that the main interest for using Cu-Hap is to enlarge the domain of water compositions for which the precipitation of meta-torbernite, (H3O)0.4Cu0.8(UO2)2(PO4)2·7.6 H2O is the predominant mechanism associated to the uranium removal, especially for pH > 6.7 where carbonate uranium species are predominant.
RESUMEN
One of the most promising approaches to laser-induced breakdown spectroscopy (LIBS) experiments involves the use of an echelle spectrometer coupled with an intensified CCD. Even if drawbacks remain with its use, the echelle spectrometer facilitates a multielemental analysis that is more rapid than can be obtained with the more-conventional Czerny-Turner spectrometer and, moreover, does not sacrifice reliability. Quantitative results obtained with such apparatus for solids, liquids, powders, and gases are described and when possible compared with results from Czerny-Turner spectrometers. Liquid analysis by LIBS with echelle spectrometers has allowed a spectral database to be compiled. Once the qualitative spectra of pure elements in aqueous solutions, are obtained, they can be used for qualitative analysis of unknown samples.
