Interpretation of X‐ray Absorption Spectra by synchrotron radiation of the uranium mineral species transported by the main stream “El Tigre”, in Peña Blanca, Chihuahua, Mexico

Abstract

The state of Chihuahua, Mexico, has several uranium deposits. The most important is the Peña Blanca deposit at north of the Chihuahua City. After an intensive exploration in the 80’s, the mineral extracted and unprocessed was confined in rock stacks exposed to weathering. To characterize the transport of uranium by surface water in the form of particles or dissolved, a sampling was carried out in the bed of the stream “El Tigre”. Nine sediment samples were collected near the Nopal 1 mine, and separated into coarse sand, fine sand, silt, and fine silt + clay fractions. The activity concentration of the uranium series isotopes was determined by gamma spectrometry, applied to the different fractions of each sample. The fine silt + clay and fine sand fractions were analyzed by X-ray diffraction in the 2 most active samples, Nopal 1 and Nopal 2. The phases are quartz, calcite, montmorillonite, sanidine, orthoclase, albite, kaolinite and magnetite. Particles of d < 100 μm (P1-Bulk) were extracted from the fine sand fraction of Nopal 1 with the help of ultraviolet light fluorescence; uranium and silicates were confirmed in them by SEM-EDS. P1-Bulk sample was subjected to X-ray absorption spectroscopy measurements on the U L3-edge, as well as to the samples fine silt + clay fraction of the Nopal 1 (P1-Clay) and Nopal 2 (P1-Silt). The X-ray absorption near edge (XANES) region analyzed indicates the presence of hexavalent uranium in the three samples. The fit of the Extended X-ray absorption fine structure (EXAFS) spectrum of the P1-Bulk sample indicates that it is α-uranophane. This result is consistent with the reports of the area.