Laser-spectroscopic studies of rare earth element- and lithium-bearing minerals and rocks

Abstract

This thesis is an interdisciplinary work, that forms a link between laser-spectroscopic and physical chemistry research to traditional geochemistry and mineralogy. The three laser-spectroscopic methods – laser-induced breakdown spectroscopy (LIBS), Raman spectroscopy, and laser-induced luminescence spectroscopy – are applied to analyse of the rare earth element (REE) and lithium- bearing mineral and rock samples collected from the European Union (EU) region. REEs and lithium were chosen as the scope of the study due to their importance to modern society and industry. The EU has determined these are critical raw materials due to their economic importance and supply risk from the EU’s perspective. The laser-spectroscopic methods presented here provide valuable information about minerals. LIBS produces a characteristic elemental emission spectrum from the mineral surface and detects all elements of the periodic table, including light and non-conductive elements. Thus, it is also very suitable for analysing precious lithium. Molecular structures and, thus, mineralogical information can be achieved with time-gated-Raman spectroscopy, which is also suitable for detecting luminescent minerals. The third compelling technique, laser-induced luminescence spectroscopy, reveals the minerals’ luminescence activators occurring even in very small concentrations. Rare earth elements can commonly act as luminescence activators. The most important characteristics of all these methods are rapid measurement time, minor (or lack of) sample preparation, the possibility of measuring solid samples, and less expensive equipment required when compared with many other techniques. Thus, all these techniques are highly suited to in situ and on-line measurement purposes, which was kept in mind while designing the analysis setups in the laboratory and the efficient data handlings.