Densities of aqueous solutions of zinc sulfate at molalities ranging from 0.1 to 3.0 mol•kg -1 were measured with a commercial vibrating tube densimeter at temperatures from 298.15 to 393.15 K and at pressures up to 10 MPa. Comparison between the present values and literature data showed a good agreement in general, however, a direct comparison could be made only at 298.15 K. Isothermal compressibilities derived from the density measurements as a function of pressure also compared favourably with literature values based on speed of sound measurements. INTRODUCTIONVolumetric properties of aqueous electrolyte solutions continue to be of great interest both academically and industrially. Accurate density and compressibility measurements can be used to give insights into ion-solvent and ion-ion interactions and are also important variables in process design 1 . Measurements performed at high temperatures and pressures can be especially useful and important in modelling hydrometallurgical and geochemical processes.Zinc, with an annual consumption of 13 to 14 million tons in the last few years, is the fourth most heavily consumed metal after iron, aluminium and copper 2 . Zinc is mainly produced by combined pyrometallurgical/hydrometallurgical routes typically involving roasting, leaching with sulfuric acid, and electrolytic recovery, or by direct leaching of zinc sulfide concentrates with sulfuric acid followed by electrowinning 3 . Nevertheless, surprisingly few experimental data exist for concentrated aqueous zinc sulfate (ZnSO4) solutions, especially at industrially relevant temperatures. Proper modelling of the volumetric properties of zinc-bearing process solutions can only be carried out if accurate data for such solutions are available for relevant temperature and concentration ranges. The most accurate density measurements of aqueous ZnSO4 solutions so far have been performed as a part of studies in ion pair formation of transition metal sulfates 4 . However, these measurements were limited to low concentrations and ambient temperatures. For modelling the hydrometallurgical processing of zinc, densities of solutions up to near-saturation and over a wide temperature range, even above the normal boiling point of water, are needed. A short summary of the existing data is given below.Gibson 5 measured densities, using a pycnometer, for 0.3 to 2.3 mol•kg -1 solutions at 298.15 K and 0.1 MPa, and also the compression of the solution volume when the pressure was increased from 0.1 MPa to 100 MPa. Purser and Stokes 6 reported density measurements with a pycnometer at concentrations from 0.01 to 2.003 mol•kg -1 at 298.15 K. Albright and Miller 7 reported pycnometric densities, in the range 0.09 to 3.6 mol•kg -1 , at 298.15 K. Lo Surdo and Millero 4 used a vibrating tube flow densimeter to measure densities in the dilute range, from 0.05 to 0.9 mol•kg -1 at 298.15 K. They also reported isentropic compressibilities κS determined from speed-of-sound measurements at 298.15 K. Apparently, the only density measurements perfo...
Internally consistent set of thermodynamic parameters was derived for the binary ZnSO4-H2O-system using the CALPHAD method. Available data on water activity, EMF measurements, solubility and heat of solution and dilution measurements was reviewed. Additional parameters for the ternary ZnSO4-H2SO4-H2O system were derived based on the available solubility and boiling point data. Solubility of zinc sulfate was predicted successfully under conditions relevant in hydrometallurgical processing of zinc, and even up to 15 mol/kg sulfuric acid solutions. Temperature dependent Pitzer parameters for the binary and ternary systems are reported.
Densities and isobaric volumetric heat capacities of aqueous solutions of the sulfate salts of cobalt(II), nickel(II) and copper(II) have been measured at 298.15 K and 0.1 MPa using vibrating tube densimetry and Picker flow calorimetry, respectively, at concentrations in the range 0.01 ≲ m/mol•kg -1 ≲ 1.5. These data were used to derive the corresponding apparent molar volumes, V, and apparent molar isobaric heat capacities, Cp.Where comparisons were possible the present V results were in good agreement with literature data. No Cp data appear to have been reported previously for any of these salts. The variations of V and Cp with concentration were well correlated using the Pitzer formalism combined with values of V o and Cp o estimated from literature data. Both V and Cp for all three salts show remarkable similarities and can be shown to lie on a common line by applying fixed addends over almost the whole concentration range studied.
Literature data for the volumetric properties of aqueous solutions of zinc sulfate have been compiled and compared with extensive recently-available measurements. A semi-empirical Pitzer model has been derived from these data that reproduces the apparent molar volumes and compressibilities of zinc sulfate solutions with good accuracy to near-saturation concentrations (m ≲ 3.0 mol•kg −1 ) over the temperature range 293.15 ≤ T/K ≤ 393.15 and at pressures up to 10 MPa, using standard volumes, V o , obtained by additivity of ionic values from the literature. By including the dependence of V o on the compressibility of pure water, the model was able to predict apparent molar volumes with good accuracy even up 100 MPa at 298 K. Of potential use for engineering applications, imposition of the inequality (∂ 2 Vϕ/∂T 2 )p,m < 0 to the Pitzer model has created the possibility of physically reasonable extrapolations to temperatures well beyond the parameterization range.
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