Data on chlorofluorocarbons (CCl3F and CCl2F2) as dating tools and hydrologic tracers in shallow ground water of the Delmarva Peninsula
No abstract available.
Delaware, Maryland, Virginia↗
Geology topics
Eurybiades Busenberg
Publications and source records attributed to Eurybiades Busenberg.
Reply to Dr. Stoesselfs comment on “Reaction paths and equilibrium end-points in solid-solution aqueous-solution systems”
In reply to the Critical Comment of R. K. Stoessell (this issue), limiting activity coefficients of bromide in halite ( γ NaBr ) have been calculated by least-squares fitting of Simons et al.'s (1952) bromide distribution coefficient data for the Na(Cl,Br)-NaOH-H 2 O system at 35°C. Regular and subregular solidsolution model fits give γ NaBr = 7.4 and γ NaBr = 8.8, respectively. The Br contents of halite at equilibrium with seawater at initial halite saturation, calculated from the regular and subregular fits, are 17 ppm and 14 ppm, respectively. A survey of literature data for trace bromide in halite shows a wide spread in distribution coefficients, with lower values ( D Br ≈ 0.01) reported by Bloch and Schnerb (1953), Puchelt et al. (1972), and Lutz (1975), and higher values ( D Br − ≈ 0.03) reported by Braitsch and Herrmann (1963), Kühn (1968), Herrmann (1972), Herrmann (1980), Mccaffrey et al. (1987), valiashko et al. (1976), Valiashko and Lavrova (1976), and Fontes (pers. commun., 1990). The measurement of stoichiometric saturation states for halite (or sylvite) with trace bromide mole-fractions is not practical, given the insensitivity of the measured solubilities on the bromide mole-fractions. Distribution coefficient measurements, with proof of thermodynamic equilibrium, need to be obtained instead, to conclusively determine the thermodynamic-mixing properties of both Na(Cl,Br) and K(Cl,Br) solidsolution series at very low mole-fractions of bromide. The applicability of the stoichiometric saturation concept to the interpretation of precipitation processes is questionable, primarily because the concept requires solid-solutions to behave as one-component solids with fixed composition. Lippmann diagrams are useful in depicting stoichiometric saturation, endmember saturation, and thermodynamic equilibrium states in binary-solid-solution aqueous-solution systems. Lippmann diagrams can contribute a better understanding of these systems, regardless of the concentration of the endmember components.
Geochimica et Cosmochimica Acta↗
Thermodynamics of magnesian calcite solid-solutions at 25°C and 1 atm total pressure
The stability of magnesian calcites was reexamined, and new results are presented for 28 natural inorganic, 12 biogenic, and 32 synthetic magnesian calcites. The magnesian calcite solid-solutions were separated into two groups on the basis of differences in stoichiometric solubility and other physical and chemical properties. Group I consists of solids of mainly metamorphic and hydrothermal origin, synthetic calcites prepared at high temperatures and pressures, and synthetic solids prepared at low temperature and very low calcite supersaturations ( ) from artificial sea water or NaClMgCl 2 CaCl 2 solutions. Group I solids are essentially binary s of CaCO 2 and MgCO 2 , and are thought to be relatively free of structural defects. Group II solid-solutions are of either biogenic origin or are synthetic magnesian calcites and protodolomites (0–20 and ∼ 45 mole percent MgCO 3 ) prepared at high calcite supersaturations ( ) from NaClNa 2 SO 4 MgCl 2 CaCl 2 or NaClMgCl 2 CaCl 2 solutions. Group II solid-solutions are treated as massively defective solids. The defects include substitution foreign ions (Na + and SO 4 2− ) in the magnesian calcite lattice (point defects) and dislocations (~2 · 10 9 cm −2 ). Within each group, the excess free energy of mixing, G E , is described by the mixing model , where x is the mole fraction of the end-member Ca 0.5 Mg 0.5 CO 3 in the solid-solution. The values of A 0 and A 1 for Group I and II solids were evaluated at 25°C. The equilibrium constants of all the solids are closely described by the equation ln , where K C and K D are the equilibrium constants of calcite and Ca 0.5 Mg 0.5 CO 3 . Group I magnesian calcites were modeled as sub-regular solid-solutions between calcite and dolomite, and between calcite and “disordered dolomite”. Both models yield almost identical equilibrium constants for these magnesian calcites. The Group II magnesian calcites were modeled as sub-regular solid-solutions between defective calcite and protodolomite. Group I and II solid-solutions differ significantly in stability. The rate of crystal growth and the chemical composition of the aqueous solutions from which the solids were formed are the main factors controlling stoichiometric solubility of the magnesian calcites and the density of crystal defects. The literature on the occurrence and behavior of magnesian calcites in sea water and other aqueous solutions is also examined.
Geochimica et Cosmochimica Acta↗
pH measurement of low-conductivity waters
pH is an important and commonly measured parameter of precipitation and other natural waters. The various sources of errors in pH measurement were analyzed and procedures for improving the accuracy and precision of pH measurements in natural waters with conductivities of < 100 uS/cm at 25 C are suggested. Detailed procedures are given for the preparation of dilute sulfuric acid standards to evaluate the performance of pH electrodes in low conductivity waters. A daily check of the pH of dilute sulfuric acid standards and deionized water saturated with a gas mixture of low carbon dioxide at partial pressure (air) prior to the measurement of the pH of low conductivity waters is suggested. (Author 's abstract)
Water-Resources Investigations Report↗
The solubility of BaCO 3 (cr) (witherite) in CO 2 -H 2 O solutions between 0 and 90°C, evaluation of the association constants of BaHCO 3 + (aq) and BaCO 3 0 (aq) between 5 and 80°C, and a preliminary evaluation of the thermodynamic properties of Ba 2+ (aq)
One hundred and fifty new measurements of the solubility of witherite were used to evaluate the equilibrium constant of the reaction BaCO 3 ( cr ) = Ba 2+ ( aq ) + CO 3 2− ( aq ) between 0 and 90°C and 1 atm total pressure. The temperature dependence of the equilibrium constant is given by log K = 607.642 + 0.121098 T − 20011.25/ T − 236.4948 log T where T is in degrees Kelvin. The log K of BaCO 3 (cr), the Gibbs energy, the enthalpy and entropy of the reaction at 298.15 K are −8.562, 48.87 kJ · mol −1 , 2.94 kJ · mol −1 and −154.0 J · mol −1 · K −1 , respectively. The equilibrium constants are consistent with an aqueous model that includes the ion pairs BaHCO 3 + (aq) and BaCO 3 0 (aq) Three different methods were used to evaluate the association constant of BaHCO 3 + (aq), and all yielded similar results. The temperature dependence of the association constant for the reaction Ba 2+ ( aq ) + HCO 3 − ( aq ) = BaHCO 3 + ( aq ) is given by log K BaHCO 3 + = −3.0938 + 0.013669 T . The log of the association constant, the Gibbs energy, the enthalpy and entropy of the reaction at 298.15°K are 0.982, −5.606 kJ · mol −1 , 23.26 kJ · mol −1 and 96.8 J · mol −1 · K −1 , respectively. The temperature dependence of the equilibrium constant for the reaction Ba 2+ ( aq ) + CO 2− 3 ( aq ) = BaCO 0 3 ( aq ) is given by log K BaCO 3 0 = 0.113 + 0.008721 T . The log of the association constant, the Gibbs energy, the enthalpy and entropy of the reaction at 298.15° K are 2.71, −15.49 kJ · mol −1 , 14.84 kJ · mol −1 and 101.7 J· mol −1 · K −1 . The above model leads to reliable calculations of the aqueous speciation and solubility of witherite in the system BaCO 3 -CO 2 -H 2 O from 0 to more than 90°C. Literature data on witherite solubility were re-evaluated and compared with the results of this study. Problems in the thennodynamic selections of Ba compounds are considered. Newer data require the revision of Δ f H° and Δ f G° of Ba 2+ (aq) to −532.5 and −555.36 kJ · mol −1 , respectively, for agreement with solubility data.
Geochimica et Cosmochimica Acta↗
The solubility of strontianite (SrCO 3 ) in CO 2 -H 2 O solutions between 2 and 91°C, the association constants of SrHCO + 3 (aq) and SrCO 0 3 (aq) between 5 and 80°C, and an evaluation of the thermodynamic properties of Sr 2+ (aq) and SrCO 3 (cr) at 25°C and 1 atm total pressure
Seventy new measurements (Sr T -P co2 of the solubility of strontianite were used to evaluate the equilibrium constant for the reaction SrCO 3 ( cr ) = Sr 2+ ( aq ) + CO 2− 3 ( aq ) between 2 and 91 °C. The temperature dependence of the equilibrium constant is given by the expression Log K = 155.0305 − 7239.594/ T − 56.58638 log T where T is in degrees Kelvin. The log K of strontianite, the Gibbs energy, enthalpy and entropy of the reaction at 25°C are −9.271 ± 0.020, 52.919 ± 0.08 kJ · mol −1 , −1.67 ± 1.30 kJ · mol −1 , and −183.1 ± 4.0 J · mol −1 · K −1 , respectively. The equilibrium constants are consistent with an aqueous model that includes the ion pairs SrHCO + 3 (aq) and SrCO 0 3 (aq) which were evaluated by potentiometric methods between 5 and 80°C. The equilibrium constant for the association reaction Sr 2+ ( aq ) + HCO − 3 ( aq ) = SrHCO + 3 aq ) is given by the expression Log K SrHCO + 3 = −3.248 + 0.014867 T . The log of the association constant, the Gibbs energy, enthalpy and entropy of the reaction at 25°C are 1.18, −6.76 kJ · mol −1 , 25.30 kJ · mol −1 , and 107.5 J · mol −1 · K −1 , respectively. The equilibrium constant for the association reaction Sr 2+ ( aq ) + CO 2− 3 ( aq ) = SrCO 0 3 aq ) is given by the expression Log K SrCO 0 3 = −1.019 + 0.012826 T . The log of the association constant, the Gibbs energy, enthalpy, and entropy of the reaction at 25°C are 2.81, −16.01 kJ · mol −1 ,21.83 kJ · mol −1 , and 126.9 J · mol −1 · K −1 , respectively. These results lead to reliable calculation of the aqueous speciation and solubility of strontianite in the system SrCO 3 -CO 2 -H 2 O from 0 to more than 90°C. Literature data on the solubility of strontianite have been evaluated and compared with these results. Our new data for strontianite have been used in an evaluation of the thermodynamic properties of Sr 2+ (aq), SrCO 3 (cr) and related compounds. The following values are recommended for the standard enthalpy (kJ · mol −1 ), Gibbs energy (kJ · mol −1 ), and entropy (J · mol −1 · K −1 ), respectively, of Sr 2+ aq): −550.90 ± 0.50, −563.83 ± 0.8 and −31.50 ± 2.0, and for SrCO 3 (cr): −1225.77 ± 1.1, −1144.73 ± 1.0 and 97.2.
Geochimica et Cosmochimica Acta↗
Chemical and X-ray analyses of 175 calcite and marble samples from the collection of the National Museum of Natural History, Smithsonian Institution
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Open-File Report↗
The solubilities of calcite, aragonite and vaterite in CO2-H2O solutions between 0 and 90°C, and an evaluation of the aqueous model for the system CaCO3-CO2-H2O
Calculations based on approximately 350 new measurements (Ca T -PCO 2 ) of the solubilities of calcite, aragonite and vaterite in CO 2 -H 2 O solutions between 0 and 90°C indicate the following values for the log of the equilibrium constants K C , K A , and K V respectively, for the reaction CaCO 3 (s) = Ca 2+ + CO 2− 3 : where T is in o K. At 25°C the logarithms of the equilibrium constants are −8.480 ± 0.020, −8.336 ± 0.020 and −7.913 ± 0.020 for calcite, aragonite and vaterite, respectively. The equilibrium constants are internally consistent with an aqueous model that includes the CaHCO + 3 and CaCO 0 3 ion pairs, revised analytical expressions for CO 2 -H 2 O equilibria, and extended Debye-Hückel individual ion activity coefficients. Using this aqueous model, the equilibrium constant of aragonite shows no PCO 2 -dependence if the CaHCO + 3 association constant is between 0 and 90°C, corresponding to the value log K Cahco + 3 = 1.11 ± 0.07 at 25°C. The CaCO 0 3 association constant was measured potentiometrically to be between 5 and 80°C, yielding log K CaCO 0 3 = 3.22 ± 0.14 at 25°C. The CO 2 -H 2 O equilibria have been critically evaluated and new empirical expressions for the temperature dependence of K H , K 1 and K 2 are , and log K 2 = −107.8871 − 0.03252849 T + 5151.79/ T + 38.92561 log T − 563713.9/ T 2 which may be used to at least 250°C. These expressions hold for 1 atm. total pressure between 0 and 100°C and follow the vapor pressure curve of water at higher temperatures. Extensive measurements of the pH of Ca-HCO 3 solutions at 25°C and 0.956 atm PCO 2 using different compositions of the reference electrode filling solution show that measured differences in pH are closely approximated by differences in liquid-junction potential as calculated by the Henderson equation. Liquid-junction corrected pH measurements agree with the calculated pH within 0.003-0.011 pH. Earlier arguments suggesting that the CaHCO + 3 ion pair should not be included in the CaCO 3 -CO 2 -H 2 O aqueous model were based on less accurate calcite solubility data. The CaHCO + 3 ion pair must be included in the aqueous model to account for the observed PCO 2 -dependence of aragonite solubility between 317 ppm CO 2 and 100% CO 2 . Previous literature on the solubility of CaCO 3 polymorphs have been critically evaluated using the aqueous model and the results are compared.
Geochimica et Cosmochimica Acta↗
The kinetics of dissolution of dolomite in CO2-H2O systems at 1.5 to 65 degrees C and 0 to 1 atm PCO2
No abstract available.
American Journal of Science↗