LITHIUM ISOTOPE FRACTIONATION DURING EXPERIMENTAL LEACHING OF LITHIUM MICAS IN VARIOUS ENVIRONMENTAL ACIDS

Transitioning to a carbon-neutral future requires an increase in mining of metals used in the green infrastructure, such as Li [1]. Lithium production has nearly tripled between 2016-2022 [2] and is projected to grow 20% annually through 2030 [3]. There is limited information on the aqueous geochemical signatures near Li deposits and the changes due to their mining [4]. Lithium is known to trigger a host of negative side effects to patients receiving Li treatment for psychological disorders, and therefore, it is important to monitor the concentration of Li, [Li], in natural waters [5]. Elevated Li concentrations have been reported in creeks and rivers near Cínovec, Czech Republic, a Li-mica deposit [6]. Further downstream, however, Li concentrations were found to be substantially lower suggesting the precipitation of clay minerals from river water, drawing down [Li]. An experiment of lepidolite mica leached in dilute sulfuric and acetic acid for 9-months showed an initial increase followed by a long-term decrease of leachate [Li] over the study period. Saturation index modeling of the leachates also suggests secondary mineral precipitation and potential drawdown mechanism of [Li] [7].

Here, we exposed two Li-micas (zinnwaldite and lepidolite) to four environmentally common acids (dilute sulfuric acid; acetic acid; oxalic acid; and deionized water) for 3 months, a point at which we reached a near-equilibrium state in previous experiment [7]. We monitored the leachate Li isotope ratio (⁷Li/⁶Li or 𝛅⁷Li) over the course of the experiment using a PerkinElmer NexION 5000 multi-quadrupole ICP-MS. Progressive evolutions of leachate 𝛅⁷Li values throughout the experiment confirms that lithium is being taken up into secondary mineral products and allow for estimates of the lithium fractionation factor involving secondary mineral products. Paired measurements of [Li] and 𝛅⁷Li values in river water downstream from Li-mica deposits and tailings sites will elucidate the fate of Li released from mining into natural systems.

[1] Choubey et al. (2016) Minerals Engineering 89.

[2] USGS (2015-2023) Mineral Commodity Summaries.

[3] Azavedo et al. (2022) Mckinsey Reports

[4] Bradley et al. (2017) USGS Report 2010-5070-0.

[5] Aral and Vecchio-Sadus (2008). Eco and Enviro Safety 70.

[6] Toupal et al. (2022) J of Geochemical Exploration 234.

[7] Toupal et al. (in prep) Applied Geochemistry.