Geochemistry and mineralogy of a spodumene-pegmatite lithium ore at various mineral beneficiation stages

Spodumene is currently the main source of lithium (Li), and Li release in mine waters stands out as a common feature of the otherwise scarcely studied spodumene mine tailings. In order to study how mineral beneficiation affects the geochemical behavior of a pegmatitic spodumene ore and the quality of its drainage, materials from the Whabouchi mine project (Québec, Canada) were submitted to advanced mineralogical characterization and kinetic testing in columns and weathering cells. Materials were sampled at various pilot processing steps, from raw ore to concentrator feed and tailings from dense medium separation and spodumene flotation. Processing did not modify markedly the chemical composition of the minerals and the mineralogical assemblage, except the spodumene content. Besides the major quartz, feldspars, spodumene, and muscovite, many accessory minerals were identified including Nb-Ta oxides and U-bearing minerals. Kinetic testing results indicate that all the studied materials produce neutral to slightly alkaline leachates (pH 7–8). Generally, elemental concentrations decrease rapidly over the first few flushes, are higher in columns than in weathering cells, and are higher for finer-grained processed materials. Elemental mobility is not necessarily proportional to bulk-rock abundance and liquid-to-solid ratio, overall following the order Ca (10 s of mg/L) > Na, K (10 s of mg/L to sub-mg/L) > Li, U (mg to sub-mg/L) > Mn, Fe, Al (sub-mg/L). Uranium mobility seems linked to scattered Ca-uranyl-(Si or P)-bearing voids and fracture-filling soluble minerals rather than primary uraninite, and Ca-uranyl-carbonate complexation is suggested as a promoting factor. Thermodynamic equilibrium calculations only identify clay minerals and metal (hydr)oxides as possible secondary minerals; formation of Al and Fe colloids is experimentally evidenced. Specific surface area and rinsing volume-normalized release rates, however, highlight effects of both processing and the testing protocol on the reactivity of the studied materials. The most processed material studied, flotation tailings, consistently produced the lowest normalized release rates for all the elements surveyed, while the most aggressive testing protocol (weathering cells, with frequent flushes at a high liquid-to-solid ratio) always yielded the highest normalized release rates. This laboratory-scale study outlines how mineralogy (both major and trace), processing, and testing protocol, affect the geochemical behavior of pegmatitic spodumene ore and tailings.