<p>The direct high-temperature leaching of α-spodumene with NaOH results in the formation of a chemically complex aqueous system. Despite the experimentally proven leachability of the mineral, variable results are reported in the literature concerning the lithium yield at specific leaching conditions. Furthermore, there is an absence of reliable data on the speciation of lithium lost in the precipitate. The high concentrations of impurities in the formed intermediate products, either solid lithium silicate or lithium hydroxide in pregnant liquor, and the extensive consumption of reagents (NaOH and CaO), consist the main drawbacks which impede the commercialization of the process. This study investigates, from a thermodynamic point of view, the effect of various parameters on lithium speciation in a real α-spodumene concentrate-NaOH–(CaO) aqueous system. Thermodynamic data were validated through the performance of experimental tests at specific conditions and the application of X-ray photoelectron spectroscopy. Lithium hydroxide and Li⁺ in the pregnant liquor and lithium silicate (Li₂SiO₃), lithium hydroxide monohydrate, lithium carbonate and lithium nitride in the residue were identified. The concentrations of NaOH and CaO and the presence of CaCO₃ as an impurity have the most intense impact on lithium release (as LiOH and Li⁺). On the other hand, the solids/liquid mass ratio and the concentration of silica as an impurity present a limited impact. The leaching conditions: 250&#xa0;°C, concentrate/NaOH/CaO mass ratio 1/2/0.5, s/l ratio 1/(4–5), silica content &lt; 20 wt.% and the minimization of CaCO₃ and nitrogen-bearing sources in α-spodumene concentrate are suggested as realistic optimal.</p> Graphical Abstract <p></p>