The apparent molal volume and compressibility of seawater fit to the Pitzer equations

摘要

The density and compressibility of seawater salt solutions for ionic strengths 0 to 0.8 m, temperatures 0-40 degrees C, and applied pressure 0 to 1000 bar are fitted to the Pitzer equations. The apparent molal volumes and compressibilities (X-phi) are fitted to equations of the form X-phi = (X) over bar(0) + A(X)I/(1.2 m) ln(1 + 1.2 I-0.5) + 2 RT m(beta((0)X) + beta((0)X)g(y) + m C-X) where I is the ionic strength, m is the molality of sea salt, A(X) is the Debye-Hiickel slope for the volume (X = V) or compressibility (X = kappa) and g(y) = (2/y(2)) [1 - (1 + y)exp(x)] where y = 2 I-0.5. The Pitzer parameters beta((0)X), beta((1)X), and C-X are fitted to functions of temperature and pressure in the form Y-X = Sigma(i) Sigma(j) a(ij)(T - T-R)P-i(j) where a(ij) are adjustable parameters, Y-X is the Pitzer parameter, T is the temperature in K, T-R = 298.15 K, and P is the applied pressure in bars (P = 0 at 1 atm or 1.013 bar). The standard deviations of the seawater fits are 8.3x10(-6) cm(3)-g(-1) for the specific volumes, 0.0007x10(-6) bar(-1) for the compressibilities, and 0.63x10(-6) K-1 for the thermal expansibilities. At 25 degrees C, the measured densities of seawater an compared to the calculated values using Pitzer coefficients for the major sea salts. The results agree with the measured values to within 45x10(-6) g-cm(-3). [References: 45]