The industrial metallurgical processing of spodumene, for the extraction of lithium hydroxide or lithium carbonate, comprises the calcination of a-spodumene to b-spodumene at 1100 ^oC followed by its leaching with sulfuric acid at 250 ^oC. Both steps are energy-intensive, while they present a high environment footprint [1]. Recent researches aim to the replacement of calcination/H₂SO₄ leaching steps by a single less energy-intensive process. Whitin this framework, among other techniques, the direct hydrothermal processing of a-spodumene, aiming to its conversion to lithium intermediate products, using sodium hydroxide at high temperature and pressure conditions, has been proposed. Despite the implemented experimental work [2-4], the literature is poor concerning the thermodynamic description of the process. Furthermore, contradictory results are presented in respect of the formed reaction products. The present study is focused on the thermodynamic study of the a-spodumene ore-NaOH system, by the using of HSC 10 software, in respect of various parameters including the: temperature, pressure, stoichiometry of the reagents and the addition of CaO as an additive. The equilibrium phase diagrams of lithium and non-lithium containing phases and, as well as, Pourbaix diagrams were conducted.