Isopiestic Determination Of The Osmotic Coefficients Of NiCl₂-NH₄Cl-H₂O

The osmotic and activity coefficient, one of the most important parameters of electrolyte, is of great significance in theoretical researches and practical applications. Nickle, an important component of a wide variety of functional materials, has many excellent qualities, such as heat-resisting, wear-resisting, high strength and high magnetic properties, and so forth. As one of the important carriers of the nickel element, the thermodynamic properties of the nickel chloride aqueous solution plays an indispensible role in metallurgy industry. This study focuses on the followings:1) Isopiestic measurements were made at308.15K for NiCl2-H2O and NH4C1-H2O aqueous solutions using NaCl(aq) as the reference standard. Then the results were represented by the Pitzer model with which the ion interaction parameters were evaluated from experimental data by multiple regressions. For NiCl2,βNiCl2(0)=0.3761,βNiCl2(1=1-2923, CNiCl2φ(0)=-0.0134; for NH4C1,βNH4Cl(0)=0.0481, βNH4Cl(0)=0.2952, CNH4Clφ(0)=-0.0026.2) Gibbs-Dehem equation was applied when trying to verify the data obtained by Pitzer Model, and the results show that for NH4C1-H2O solution, Pitzer Model is reliable under the whole range of test concentration. For NiCl2-H2O, the results are less approving when the concentration of NiCl2is very low.3) Isopiestic measurements were made at308.15K for NiCl2-NH4Cl-H2O solutions using NaCl(aq) as the reference standard. Then the results were represented by the Pitzer model with which the ion interaction parameters for mixed electrolytes were evaluated from experimental data by multiple regressions, and the values are as follows:θ=-0.0260,ψ=-0.0231.4) ECA model was resorted to calculate the activity of water of the NiCl2-NH4Cl-H2O solutions, and the parameters were obtained, with λ=0.00267,δ=-0.00026. 5) ECA model has been modified which contains three parameters for NiCl2-NH4Cl-H2O, and the parameter has been fitted with k1=-0.00682;k2=0.00114; k3=-0.00014.6) The comparison of the results of activity of water which is based on Pitzer Model, ECA model and ECA-modified model were made, and it shows that Pitzer model is the best model for NiCl2-NH4Cl-H2O when considering about its water activity, and then is the ECA-modified model with only slightly better than ECA model.