Experimental leaching of lithium ores in simulated environmental conditions

Abstract

Leaching experiments were performed on zinnwaldite-rich greisen, pure zinnwaldite separated from the greisen, spodumene pegmatite, and pure lepidolite in dilute sulfuric, acetic, and oxalic acids (all 0.01 M) as well as deionized water to simulate common environmental conditions. The experiments were carried out at room temperature over a period of 267 days (9 months). Considerable amounts of Li, Al, and Fe (up to 0.76 mM, 6.60 mM, and 0.87 mM, respectively) were observed in the leachates as a result of Li-mica dissolution. The dissolution time-series trends of [SiO₂], [Al] and [Li] for the whole-rock zinnwaldite-greisen and the pure zinnwaldite separate are nearly identical, suggesting preferential dissolution of zinnwaldite in the greisen host rock. Lepidolite released the highest amounts of SiO₂ and Al into the solution, but it also has the smallest grain size and largest specific surface area of the studied samples. Lepidolite samples further show decreasing [Li] in the sulfuric and acetic acid leachates. Spodumene pegmatite released the smallest amounts of analytes in each experiment, except for Fe. Using SEM-EDX, backscattered electron images, and powder XRD, we observed and identified precipitates of secondary quartz resulting from Li-mica dissolution, as predicted by our geochemical modeling. Even though elpasolite was not observed using the SEM, the mineral was detected in some samples via XRD, suggesting that large amounts of F were present in these leachates. We conclude that enhanced weathering of Li-mica deposits due to their development and mining may lead to a considerable influx of Li, Al, and F into surface waters in adjacent areas.