Experimental Determination of CoSO4–Li2SO4–H2O Ternary Phase Diagram between 283.15 and 323.15 K

Solid–liquid equilibria of the ternary CoSO₄–Li₂SO₄–H₂O chemical system have been determined at T = 283.15, 298.15, 308.15, and 323.15 K using discontinuous isoperibolic thermal analysis, inductively coupled plasma–optical emission spectrometry, and X-ray powder diffraction. The phase diagram that has been experimentally constructed details the evolution of the solubility according to the chemical composition and temperature. The studied chemical system is characterized by solid-brine equilibria involving only simple salts. This makes it possible to define ranges of composition favoring the precipitation of one type of salt over another and thus to separate them by selective crystallization according to a starting composition. It also suggests that in a specific domain of composition, it is possible to crystallize either CoSO₄.nH₂O (n = 6 or 7 depending on temperature) or Li₂SO₄.H₂O by increasing or decreasing the temperature. This is due to the opposite behavior of their solubility as a function of temperature. This work proposes a set of experimental data (solubilities, polysaturated points, and boundaries between triphasic and biphasic domains) that could be used to be integrated into a thermodynamic model.