Title
Spectroscopic Studies of Mössbauer, Infrared, and Laser-Induced Luminescence for Classifying Rare-Earth Minerals Enriched in IronRich Deposits
Author
Noboru Aoyagi, Thuy T. Nguyen, Yuta Kumagai, Tung V. Nguyen, Masami Nakada, Yukari Segawa, Hung T. Nguyen, Thuan Ba Le
Year
2020
Journal
ACS Omega
Abstract
Rare-earth (RE) phosphates often appear as an accessory
phase in igneous or metamorphic rocks; however, these rocks are composed
of myriad chemical elements and nuclides that interfere with the qualitative
or quantitative analyses of the RE phosphates over a range of concentrations
in the absence of a pretreatment. In addition, the limit of each analytical
methodology constrains the approach as well as the usefulness of the results
in geoscience applications. Here, we report the specific mineral characterization of RE-containing ores from Yen Phu mine, Vietnam, using a range of
state-of-the-art spectroscopic techniques in conjunction with microscopy:
Mössbauer spectroscopy, infrared microspectroscopy, time-resolved laserinduced fluorescence spectroscopy (TRLFS), and scanning electron
microscopy with energy-dispersive X-ray spectroscopy. Because the distribution of each element in the deposit differs, such
combinatorial works are necessary and could lead to more plausible answers to questions surrounding the point of origin of RE
elements. The results of our Mössbauer spectroscopic analysis indicate that the three ores sampled at different locations all contain
magnetite-like, hematite-like, and iron(III) salts other than hematite. In addition, we confirmed the presence of phosphate around
the grain boundary in the magnetite-like mineral phase by infrared microspectroscopic analysis. The present analytical findings of
trace amounts of europium(III) using TRLFS suggest that the europium ions generate identical luminescence spectra despite being
embedded in three different matrices of iron minerals. This demonstration highlights the benefits of combinatorial spectroscopic
analyses to gain insights into the effects of the environment of REs on their solid-state chemistry and shows the potential utility of
TRLFS as a resource mining tool. Further applications of this approach in the analytical screening of rocks and minerals are feasible
Instrument
IRT-5200
Keywords
Rare-Earth Minerals Enriched, FTIR microscopy, Iron Deposits