Metal(loid) mobility, solid-phase speciation and in vitro bioaccessibility in European hard-rock lithium (Li) deposits

Abstract

The European Union (EU) lags in lithium (Li) production despite having substantial resources in pegmatites and rare-metal granites. To address this, the European Commission has encouraged Li mining in Europe. However, there is limited information about the potential environmental and human-health impacts associated with Li mining from these lithologies. In this study, we assess the mobility, solid-phase speciation, and in vitro bioaccessibility of metal(loid)s by combining a series of leaching tests with mineralogical analyses on Li-rich ore and process samples. Despite relatively high concentrations of metal(loid)s such as As, Cr, Ni, and Zn, laboratory leaching tests simulating weathering under environmental conditions reveal generally low mobility for most metal(loid)s, much lower than the reference thresholds. Lithium, for which no threshold values are currently available, exhibits higher mobility (up to ca. 62 mg/kg in the toxicity characteristic leaching procedure) due to the greater alterability of Li minerals. Spatially-resolved mineralogical analyses and pH-dependent leaching tests reveal that metal(loid)s are primarily hosted in sulfides (arsenopyrite, chalcopyrite, sphalerite) and chromite. Detailed in situ mineralogical investigations using LA-ICP-MS demonstrate the presence of metal(loid)s as traces in common silicates (biotite, muscovite) and fluorapatite, underscoring the complexity of metal(loid) solid-phase speciation in these materials. The in vitro oral bioaccessibility of the metal(loid)s is low to moderate (< 35 %). Inverse geochemical modeling indicates that the mobility of metal(loid)s primarily results from the dissolution of silicates and phosphates containing low amounts of metal(loid)s at low pH (0.5–2). The metal(loid) in vitro gastric bioaccessibility also stems from the dissolution of these minerals with low metal(loid) contents. Non-carcinogenic and carcinogenic risk assessments corrected for in vitro bioaccessibility indicate low health risks. However, given the limited knowledge on Li (eco)toxicity, implementing the best practices for tailing managements is warranted to limit human and environmental exposure.