The solubility of zinc oxide in 0.03 m NaTr as a function of temperature, with in situ pH measurement

The solubility of zincite (ZnO) has been measured in noncomplexing solution s over a wide range of pH(m) (4-11), and temperature (75-200 degrees C) at 0.03 mol.kg(-1) ionic strength in NaTr media (sodium trifluoromethanesulfon ate, a noncomplexing 1:1 electrolyte), in a hydrogen electrode concentratio n cell (HECC), which provided continuous in situ measurement of hydrogen io n molality. Total zinc content was analyzed by atomic absorption using graphite furnace , flame, and inductively coupled plasma (ICP) spectrometers. The direction of approach to the equilibrium saturation state was varied to demonstrate t hat the system was reversible thermodynamically. Separate experiments were performed in alkaline solutions (0.03 mol . kg(-1) NaOH) at 25 and 50 degre es C in polypropylene syringes, and between 50 and 290 degrees C in a Teflo n-lined pressure vessel. The aim of these experiments was to reach higher p H(m) (>8 depending on the temperature) to determine the thermodynamic prope rties of the negatively charged species, Zn(OH)(3)(-). A least-squares regr ession of the results obtained at this ionic strength was used to determine the molal solubility products (Q(sn)) of zincite. The solubility products (Q(sn)) were extrapolated to infinite dilution (K-s n), permitting calculation of the thermodynamic properties of aqueous speci es of zinc for comparison with previous work. Copyright (C) 1999 Elsevier S cience Ltd.