Thermodynamic Properties of Aqueous Zinc Sulfate Solutions under Super- ambient Conditions: A Novel Approach

Abstract

Abstract A new method has been proposed to estimate the osmotic and activity coefficients of aqueous electrolyte solutions under super-ambient conditions on the basis of the Pitzer ion-interaction approach using the volumetric data. Following this method, a compact set of Pitzer ion-interaction parameters, βMX(0), βMX(1), βMX(2), and βMXϕ, valid within the temperature range from 293.15 to 373.15 K, and pressure range from 0.1 to 10 MPa have been obtained for aqueous ZnSO4 solutions. These parameters helped evaluate the osmotic and activity coefficients of this system to 3.0 mol∙kg− 1 within the temperature and pressure range mentioned above. The pressure dependences of osmotic and activity coefficients have also been estimated using the equations derived by Rogers and Pitzer (1982). The results obtained by the method proposed in this research agree very well with those calculated using Rogers & Pitzer approach. The advantage of the method proposed here is that it directly provides a compact set of Pitzer ion-interaction parameters required for describing the osmotic and activity coefficients, in contrast to the other method. This study also provided important information as to the ion-association behaviour of aqueous ZnSO4 solution with respect to temperature and pressure. Further, the apparent molar enthalpies have been estimated using appropriate temperature derivatives of the Pitzer ion-interaction parameters.