THE IMPACT OF GEOLOGICAL ENVIRONMENT ON THE LITHIUM CONCENTRATION AND STRUCTURAL COMPOSITION OF HECTORITE CLAYS

Lithium has become a technologically important metal, being used more and more in rechargeable batteries, electric vehicles and advanced technologies for its energy efficiency. It is found in low concentration in soils and rivers, and is enriched in certain minerals and brines. Hectorite is a Li-rich clay with known concentrations varying from 0.16% to 0.74% Li, where Li occurs both in the octahedral and the interlayer sites of the mineral structure. It can form either authigenically or as an alteration product under both low temperature and hydrothermal conditions. The objective of this research is to characterize the Li concentration and structural composition of hectorites from 4 sites in the western USA believed to have formed under different conditions.

A suite of 18 samples was collected for this research: 6 samples from Clayton Valley NV and 1 sample from Fish Lake Valley NV, believed to have form under low temperature conditions (<100°C); 1 sample from Hector CA and 9 samples from McDermitt NV, believed to have formed under elevated temperature conditions (>100°C); and 1 sample of synthetic hectorite. All samples were cleaned to concentrate the clay fraction and remove the non-clay minerals. Random X-ray diffraction (XRD) profiles indicate that most of the impurities were removed from the samples. These profiles, along with basal-oriented XRD profiles (air-dried and glycolated) show the majority of the clays to be smectites, with a few of the McDermitt samples having an illite signature and the Clayton Valley samples showing a mixture of smectite/illite. The Li concentration of the purified clay samples varies from 0.1% Li in Clayton Valley to 1.2% Li in McDermitt. Most samples, excluding Clayton Valley, are Mg-rich (>10% Mg) and Al-poor (<3% Al) and have high fluorine concentrations (up to 6.5% F).

Results of this research will have implications for evaluating clays as a source of Li. Identifying the location of Li in the hectorite structure will help the mining industry investigate effective extraction of Li from hectorite, while linking Li content with depositional environment will guide exploration for potentially economic hectorite deposits. This research will also contribute to understanding the global geochemical cycle of Li.