Process Mineralogy of Li-Enriched Pegmatite Combining Laboratory Mineral Separations and SEM-Based Automated Image Analysis

Abstract

Brazil has 95 million tons of Li reserves in the form of pegmatites but produces less than 1% of the global output. Historically Li production in Brazil has been low due to governmental restrictions aimed at controlling the exploitation and trade of Li in Brazil. However, as of 2022, these restrictions were revoked. The abundance of untapped pegmatite ores in Brazil complements the soaring demand for Li in energy-storage applications. This study performs process mineralogy studies on 10 samples collected from a Li pegmatite deposit in the southeastern region of Minas Gerais in Brazil. The samples were characterized by combining density separation and SEM-based automated mineralogy processing system allied with XRF, ICP OES, XRD, and LA–ICPMS. The latter was used to determine Li content in micas which allowed determining the Li deportment between Li-bearing minerals. The results show that the samples contain such Li-bearing minerals as muscovite (0.5 wt% Li2O) and lepidolite (3.1 wt% Li2O), in addition to spodumene (8.0 wt% Li2O). According to the characterization of the spodumene concentrate (d = 3.11) by density separation (at d = 2.95), two main trends were observed: (a) low Li deportment in the sink product (approximately 44% wt%) and higher Li2O grade (approximately 6.5 wt%), and (b) higher Li deportment in the sink product (58%) and lower Li2O content (approximately 4.9 wt%). The first trend is associated with higher modal content of mica since it carries Li to the light product. Lower Li grade is related to the presence of Fe-bearing minerals (e.g., epidote and amphibole) as they report to the dense product and do not contain Li. Spodumene has a high degree of liberation in all samples; therefore, it did not influence the deportment results. The findings highlight the benefit of combining scanning electron microscopy-based automated mineralogy with LA–ICPMS and other techniques from process mineralogy studies in mineral processing. In addition to the mineralogy and liberation characteristics, identifying Li-bearing minerals and determining Li deportment is crucial.