Determination And Study Of The Vapor Pressures And The Isobaric Heat Capacities Of The Alkaline Sodium Aluminate Solutions

The alkaline sodium aluminate solutions play an important role in the process of alumina production, and much geochemical process also involves its physicochemical properties, especially the thermodynamics property. Therefore, the thermodynamics properties of Na2O-Al2O3-H2O have an important role in the production practice. The research work is as follows:1. The vapor pressures of the alkaline sodium aluminate solutions were measured at different concentrations (wNaOHT (mNaOHT/mNaAl(OH)4)=1.3120～4.3490mol·kg-1, ak (mNaOHT/mNaAl(OH)4)=2.0783～5.8557) and temperatures from303.15K to313.15K by a differential static method.The osmotic coefficients and water activities were calculated. The data determined have been represented by the Pitzer’s model by using multiple regressions. According to Pitzer’s model, the water activities of the ternary system were calculated, and their variations with ionic strength were established by calculations.2.The isobaric heat capacities of the alkaline sodium aluminate solutions have been measured in a commercial calorimeter (Setaram C80) using discrete (step-by-step) increases of temperature interspersed with isothermal equilibration periods at temperatures ranging from298.15K to363.15K at constant pressure, where the total alkli molality mNaOHT and ak are6.652～12.0545mol·kg-1and5.0304-6.7387, respectively. The relational model of the isobaric heat capacities as a function of mNaOHY,αk, and temperature was established for the alkaline sodium aluminate solution with the data from the literature reported. The experimental data of the isobaric heat capacities measured and calculated by using the model are in reasonable agreements, where the errors are less than0.0069. The apparent molar heat capacities for sodium aluminate solution were also calculated, and the results show that the change rule correspond with the Young’s Law.