Uranyl-evansites from Porto (northwest Portugal) and Galicia (northwest Spain): structure and assignment of spectra catholuminescence and Raman bands

Abstract

Uranyl-evansites from Porto (Northwest Portugal) together with historical evansite standards from Galicia (Northwest Spain), Slovakia, and Congo were studied by Environmental Scanning Electron Microscopy (ESEM), Energy Dispersive Spectrometry (EDS), Back-Scattering (BS), Spectra Cathodoluminescence (CL), Micro-Raman and X-Ray Diffraction (XRD), and Inductively Coupled Plasma Mass Spectrometry (ICP-MS). This work mainly focused on Porto's evansites collected from the urban underground, looking for uranyl groups and the subsequent air radon gas levels in hypogeal environments, for example, from 6000 to 7000 Bq/m3. Evansite (Al3(PO4)(OH)6 · 6H2O) comprises microlayers of amorphous hydrous aluminum-phosphate phases together with hydrolyzed uranyl groups and hydroxide UO2(OH)2 precipitates. The studied evansites contain uranyl groups reaching up to UO2 0.78% in the case of Kobokobo, as detected by EDS and CL, and 0.1% in the Porto samples, as detected by CL and ICP-MS. The CL spectra probe is a very fast tool in detecting uranyl groups. Raman spectra of evansites are homogeneous in samples from different localities and not previously published. Therefore, we suggest Zeleznik-type evansite as a new representative international Spectrum Raman pattern for evansite.