Geology topics
P. B. Hostetler
Publications and source records attributed to P. B. Hostetler.
A thermostatic water bath for experimental studies in aqueous solutions
A temperature-controlled water bath for the study of ion-pairing equilibria and mineral solubility in aqueous solutions below 100°C is described. The bath is similar to a previously described system (P. B. Hostetler and C. L. Christ, 1968, U.S. Geol. Survey Prof. Paper 600-D, p. D217-D221) but incorporates several significant improvements. Included among these are a more efficient stirring mechanism, a potentially larger solid-to-solution ratio, and improved equilibration of the gas phase with the solution.
Activity-product constants of brucite from 10 degrees to 90 degrees C
The activity-product constant of brucite, K B = [Mg 2+ ][OH - ] 2 (where the brackets denote activities), was determined experimentally at 10°, 25°, 40°, 55°, 70°, and 90°C. The values obtained for -log K B are 10.89±0.16 (10°), 10.88±0.10 (25°), 10.90±0.10 (40°), 10.90±0.10 (55°), 10.99±0.14 (70°), and 11.10±0.14 (90°). Using National Bureau of Standards Technical Note 270 data for the ions, the free energy of formation (Δ G ° t ) at 25° for brucite is 831.486 joules per mole ( 198,730 cal mol -1 ). Using data compiled by R. A. Robie and D. R. Waldbaum in 1968 for the ions, this Δ G ° t is -823,323 J mol -1 (-198,930 cal mol -1 ). Values of log KB are also calculated for the temperature range 0° to 200°C, by using thermochemical data listed by V. B. Parker, D. D. Wagman, and W. H. Evans in 1971 and E. G. King, M. J. Ferrante, and L. B. Pankratz in 1975 and the partial molal heat capacities estimated by C. M. Criss and J. W. Cobble in 1965. The experimental values are similar to the calculated values, especially at lower temperatures.
Stabilities of calcite and aragonite
A revaluation of the 25° C activity-product constants of calcite ( K C ) and aragonite ( K A ) was made on the basis of the known solubilities of these phases for which the activity of total dissolved calcium was corrected for the presence of the ion pair CaHCO 3 + in the aqueous phase. The value of the dissociation constant of CaHCO 3 + was taken to be 10 -1.225±0.02 . This value, combined with values of the analytical concentrations in solutions with partial pressure P CO2 =0.97 atmosphere, leads to K C =l0 -8.52±0.04 and K A = 10 -8.36±0.04 . Based on these K values, standard free energies of formation of calcite and aragonite were calculated to be -270,144±375 and -269,926±375 calories mole -1 , (-1,130,282±1,569 and -1,129,370±1,569 joules mole -1 ), respectively. From the 25°C K values, using appropriate entropy and heat capacity data, values of K C and K A were calculated over the temperature range 0° to 200°C. Possible errors in interpretation of measured pH values and inferred P CO2 values and the bearing of these errors on calculations of K values are discussed.
Activity-product constants of aragonite at 90° and 51°C
The activity-product constants of aragonite, K A =[Ca 2+ ][CO 3 2- ] (where the brackets denote activities), were determined experimentally at 90°C and at 51°C. Results at 90°C were obtained from four separate dolomite dissolution runs, in which aragonite precipitated and came to equilibrium with the aqueous phase (from the direction of. supersaturation), and from two runs starting with aragonite suspended in dilute MgCl 2 solutions (from the direction of undersaturation). The average values of K A from the six runs were in excellent agreement; for the negative logarithm of K A , P K A , they yield a value of 8.95±0.05. One run was made at 51° C starting with aragonite suspended in dilute MgCl 2 solution; the value of p K A at 51°C is 8.61±0.05. No X-ray detectable calcite was found at the conclusion of any of the runs, including a dolomite dissolution run at 90°C (D-10) that was sampled over a period of 10,268 h and toward the end had a concentration of approximately 0.002 molal total dissolved magnesium.
Studies in the system MgO-SiO2-CO2-H2O(I): The activity-product constant of chrysotile
Chrysotile dissolves congruently in water according to the reaction: Mg 3 Si 2 O 6 ( OH ) 4 c + 5 H 2 O l = 3 Mg aq 2+ + 6 OH aq − + 2 H 4 SiO 4 aq . Experimental determination of the activity-product constant of chrysotile, K chr = [ Mg 2+ ] 3 [ OH − ] 6 [ H 4 SiO 4 aq ] 2 , at 90°C, yields the value of K chr = 10 −49.2 ± 10 0.5 . A synthetic sample and a natural sample from New Idria, California, were used in the determination. Values of K chr were calculated for temperatures ranging from 0°C to 200°C, using the thermochemical data of King et al . (1967) for chrysotile and antigorite, various solubility data for silica, and ionic partial molal heat capacities estimated by the method of criss and Cobble (1964a). K chr is 10 −54.1 at 0°C, rises to a maximum value of 10 −48.5 at approximately 135°C, and is 10 −49.1 at 200°C (all values for the three-phase system, chrysotile plus solution plus vapor). The calculated 90°C value is 10 −49.1 , in excellent agreement with the experimental value; for 25°C, the calculated value is 10 −50.8 .
Dissociation constants of KSO 4 - from 10°-50°C
A cell without liquid junction was used to obtain dissociation constants for the reaction: KSO 4 − = K + + SO 4 2− . At 10°, 25°, 38° and 50°C, values for K diss KSO 4 − are, respectively, 0.19 5 , 0.14 2 , 0.11 7 , and 0.09 5 . At 25°C, , and values for the KSO 4 − ion are −245.96 and −274.02 kcal mole −1 , and S ° is +42.3 cal mole −1 deg −1 .
Activity coefficients of aqueous potassium chloride measured with a potassium-sensitive glass electrode
Values of γ ±KCl over temperature and molality ranges of 10° to 50°C and 0.01 to 1.0 molal were determined with an electromotive-force cell: potassium-sensitive glass electrode, KCl (molality), Ag-AgCl. A more satisfactory method than is commonly employed was devised for treating the experimental measurements of potential.