THE SOLUBILITY OF ZINC OXIDE IN 0.03 M NATR AS A FUNCTION OF TEMPERATURE, WITH IN SITU PH MEASUREMENT

Abstract

The solubility of zincite (ZnO) has been measured in noncomplexing solutions over a wide range of pHm (4-11), and temperature (75-200°C) at 0.03 mol . kg-1 ionic strength in NaTr media (sodium trifluoromethanesulfonate, a noncomplexing 1:1 electrolyte), in a hydrogen electrode concentration cell (HECC), which provided continuous in situ measurement of hydrogen ion 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 that the system was reversible thermodynamically. Separate experiments were performed in alkaline solutions (0.03 mol . kg-1 NaOH) at 25 and 50°C in polypropylene syringes, and between 50 and 290°C in a Teflon-lined pressure vessel. The aim of these experiments was to reach higher pHm (>8 depending on the temperature) to determine the thermodynamic properties of the negatively charged species, Zn(OH)3-. A least-squares regression of the results obtained at this ionic strength was used to determine the molal solubility products (Qsn) of zincite.The solubility products (Qsn) were extrapolated to infinite dilution (Ksn), permitting calculation of the thermodynamic properties of aqueous species of zinc for comparison with previous work.