Alteration of spodumene (LiAlSi2O6) and its impact on the recovery of lithium

Johannes Chischi

The battery metal lithium is crucial to the green energy transition and increasing global demand accelerates the exploitation of spodumene-bearing LCT-pegmatites as a source of lithium. High-grade spodumene concentrates are required to produce battery-grade lithium chemicals but, as illustrated by an abundance of green spodumene pseudomorphs, spodumene is subject to alteration. Despite profound effects on ore quality and lithium recovery, spodumene alteration has not yet been documented in detail. Post-magmatic alteration converts initially white-grey, hard spodumene into fine-grained, silky-soft green or dark green pseudomorphs consisting of muscovite (KAl3Si3O10(OH)2) and cookeite (LiAl5Si3O10(OH)8). Exposure of these secondary phases to high temperatures during conventional calcination leads to melting and the formation of an amorphous glass phase. The glass covers β-spodumene particles and reduces lithium recovery during subsequent sulphuric acid baking. Lithium recovery is negatively correlated with secondary phase content, which may serve equally well or better as an indicator of spodumene concentrate quality than the conventionally used Fe2O3 content. Spodumene alteration occurs because of auto-metasomatism of primary pegmatite minerals by an aqueous fluid that is exsolved from the pegmatite melt. Oxygen isotope equilibria and the composition of primary muscovite suggest that the primary pegmatite assemblage has formed at around 457 ± 50 °C from a highly evolved melt. The alteration of spodumene is associated with albitisation of microcline (KAlSi3O8) that provides K for the formation of secondary muscovite at temperatures below 350 °C. Fluids migrate along spodumene grain boundaries, cracks, and cleavage planes to create pseudomorphic spodumene replacement textures and primarily reflect a magmatic origin. The extent of green spodumene at the study site is limited but the post-magmatic alteration process can completely eradicate mineralisation from spodumene pegmatites. A method based on Raman mapping is developed for the quantification of mineral impurities in spodumene ores and concentrates, as well as to monitor conversion rates of α- to β-spodumene. The new method demonstrates higher accuracy and a lower muscovite quantification limit than conventional Rietveld refinement of XRD data making it a versatile alternative for quality control. This PhD thesis highlights the detrimental effect of spodumene alteration on ore and concentrate quality as well as lithium recovery during conventional metallurgical extraction. Furthermore, it documents the conditions that lead to the alteration of spodumene in a typical LCT-pegmatite and provides an alternative method for quantification of alteration-associated impurities by Raman mapping.

Alteration of spodumene (LiAlSi2O6) and its impact on the recovery of lithium

Files and links (1)

Abstract

Details

Metrics