Handheld LIBS analysis for in situ quantification of Li and detection of the trace elements (Be, Rb and Cs)

Abstract

The world's lithium demand is currently increasing due to its use in batteries and in green energy technologies. As a consequence, Li has recently been added to the list of critical materials in Europe. Finding new deposits is necessary in order to guarantee a mid- to long-term stable supply. Granites and associated pegmatites are the primary ‘hard-rock’ source for Li, where it is present in a variety of aluminosilicate minerals. Li is a light element that typically occurs at low concentrations in rocks and minerals, which presents challenges for some analytical techniques (e.g., portable X-ray fluorescence) for exploration. Laser induced breakdown spectroscopy (LIBS) is a powerful analytical technique for the acquisition of simultaneous almost all elements of the periodic table. LIBS has particular sensitivity to the light elements (Z < 13) and, therefore, handheld LIBS has significant potential for the exploration of pegmatite- or granite-related Li mineralization. For this study, a suite of 16 pegmatite-hosted Li ore minerals comprising the three main aluminosilicate species (spodumene, lepidolite and petalite) that contained between 1.36 and 3.54 wt% Li was analyzed using a handheld LIBS instrument. A univariate calibration curve was developed for LIBS quantification of Li in these minerals using the strong Li emission lines at 610.36 nm and 670.79 nm (R2 > 0.9, RMSD = 0.2 wt% Li). Simultaneous quantification of Li contents and measurement of major element ratios (e.g., Si/Al) using portable LIBS permits rapid discrimination between different Li-bearing silicates, such as spodumene and petalite, that can be difficult to identify in the field on the basis of macroscopic criteria. Moreover, the detection of minor/trace elements such as Be, Rb and Cs is possible by handheld LIBS, which can provide useful information for rare metal pegmatite and granite exploration. Thus, qualitative and quantitative analysis by handheld LIBS represents a very promising approach for Li exploration.