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1.
Melchor González-Dávila J. Magdalena Santana-Casiano Frank J. Millero 《Aquatic Geochemistry》2007,13(4):339-355
The thermodynamic stability constants for the hydrolysis and formation of mercury (Hg2+) chloride complexes
have been used to calculate the activity coefficients for Hg(OH)
n
(2–n)+ and HgCl
n
(2–n)+ complexes using the Pitzer specific interaction model. These values have been used to determine the Pitzer parameters for
the hydroxide and chloro complexes and C
ML). The values of and have been determined for the neutral complexes (Hg(OH)2 and HgCl2). The resultant parameters yield calculated values for the measured values of log to ±0.01 from I = 0.1 to 3 m at 25°C. Since the activity coefficients of and are in reasonable agreement with the values for Pb(II), we have estimated the effect of temperature on the chloride constants
for Hg(II) from 0 to 300°C and I = 0–6 m using the Pitzer parameters for complexes. The resulting parameters can be used to examine the speciation of Hg(II) with Cl− in natural waters over a wide range of conditions. 相似文献
2.
We present a theoretical model for diffusive daughter isotope loss in radiochronological systems with increasing temperature.
It complements previous thermochronological models, which focused on cooling, and allows for testing opening and resetting
of radiochronometers during heating. The opening and resetting temperatures are, respectively,
where R is the gas constant, E and D
0 are the activation energy and the pre-exponential factor of the Arrhenius law for diffusion of the daughter isotope, a the half-size of the system (radius for sphere and cylinder and half-thickness for plane sheet) and τ the heating time constant, related to the heating rate by
For opening and resetting thresholds corresponding to 1 and 99% loss of daughter isotope, respectively, the retention parameters
for sphere, cylinder and plane sheet geometries are A
op = 1.14 × 105, 5.07 × 104 and 1.27 × 104 and A
rs = 2.40, 1.37 and 0.561. According to this model, the opening and resetting temperatures are significantly different for most
radiochronometers and are, respectively, lower and higher than the closure temperature.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
3.
Kinetic experiments of dolomite dissolution in water over a temperature range from 25 to 250°C were performed using a flow
through packed bed reactor. Authors chose three different size fractions of dolomite samples: 18–35 mesh, 35–60 mesh, and
60–80 mesh. The dissolution rates of the three particle size samples of dolomite were measured. The dissolution rate values
are changed with the variation of grain size of the sample. For the sample through 20–40 mesh, both the release rate of Ca
and the release rate of Mg increase with increasing temperature until 200°C, then decrease with continued increasing temperature.
Its maximum dissolution rate occurs at 200°C. The maximum dissolution rates for the sample through 40–60 mesh and 60–80 mesh
happen at 100°C. Experimental results indicate that the dissolution of dolomite is incongruent in most cases. Dissolution
of fresh dolomite was non-stoichiometric, the Ca/Mg ratio released to solution was greater than in the bulk solid, and the
ratio increases with rising temperatures from 25 to 250°C. Observations on dolomite dissolution in water are presented as
three parallel reactions, and each reaction occurs in consecutive steps as
where the second part is a slow reaction, and also the reaction could occur as follows:
The following rate equation was used to describe dolomite dissolution kinetics
where refers to one of each reaction among the above reactions; k
ij
is the rate constant for ith species in the jth reaction, a
i
stands for activity of ith aqueous species, n is the stoichimetric coefficience of ith species in the jth reaction, and define . The experiments prove that dissolved Ca is a strong inhibitor for dolomite dissolution (release of Ca) in most cases. Dissolved
Mg was found to be an inhibitor for dolomite dissolution at low temperatures. But dissolution rates of dolomite increase with
increasing the concentration of dissolved Mg in the temperature range of 200–250°C for 20–40 mesh sample, and in the temperature
range of 100–250°C for 40–80 mesh sample, whereas the Mg2+ ion adsorption on dolomite surface becomes progressively the step controlling reaction. The following rate equation is suitable
to dolomite dissolutions at high temperatures from 200 to 250°C.
where refers to dissolution rate (release of Ca), and are molar concentrations of dissolved Ca and Mg, k
ad stands for adsorption reaction rate constant, K
Mg refers to adsorption equilibrium constant.
At 200°C for 40–60 mesh sample, the release rate of Ca can be described as:
相似文献
4.
Yongliang Xiong 《Aquatic Geochemistry》2008,14(3):223-238
Solubility experiments were conducted for the dissolution reaction of brucite, Mg(OH)2 (cr):
Experiments were conducted from undersaturation in deionized (DI) water and 0.010–4.4 m NaCl solutions at 22.5°C. In addition,
brucite solubility was measured from supersaturation in an experiment in which brucite was precipitated via dropwise addition
of 0.10 m NaOH into a 0.10 m MgCl2 solution also at 22.5°C. The attainment of the reversal in equilibrium was demonstrated in this study. The solubility constant
at 22.5°C at infinite dilution calculated from the experimental results from the direction of supersaturation by using the
specific interaction theory (SIT) is: with a corresponding value of 17.0 ± 0.2 (2σ) when extrapolated to 25°C. The dimensionless standard chemical potential (μ°/RT)
of brucite derived from the solubility data in 0.010 m to 4.4 m NaCl solutions from undersaturation extrapolated to 25°C is
−335.76 ± 0.45 (2σ), with the corresponding Gibbs free energy of formation of brucite, , being −832.3 ± 1.1 (2σ) kJ mol−1. In combination with the auxiliary thermodynamic data, the is calculated to be 17.1 ± 0.2 (2σ), based on the above Gibbs free energy of formation for brucite. This study recommends
an average value of 17.05 ± 0.2 in logarithmic unit as solubility constant of brucite at 25°C, according to the values from
both supersaturation and undersaturation.
Sandia National Laboratories is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the
United States Department of Energy’s National Nuclear Security Administration under Contract DE-AC04-94AL85000. 相似文献
5.
The temperature-sensitive Fe,Mg exchange equilibrium,
相似文献
6.
Alexej N. Platonov Klaus Langer Stanislav S. Matsyuk 《Physics and Chemistry of Minerals》2008,35(6):331-337
In the course of a thorough study of the influences of the second coordination sphere on the crystal field parameters of the
3d
N
-ions and the character of 3d
N
–O bonds in oxygen based minerals, 19 natural Cr3+-bearing (Mg,Ca)-garnets from upper mantle rocks were analysed and studied by electronic absorption spectroscopy, EAS. The
garnets had compositions with populations of the [8]
X-sites by 0.881 ± 0.053 (Ca + Mg) and changing Ca-fractions in the range 0.020 ≤ w
Ca[8] ≤ 0.745, while the [6]
Y-site fraction was constant with x
Cr3+
[6] = 0.335 ± 0.023. The garnets had colours from deeply violet-red for low Ca-contents (up to x
Ca = 0.28), grey with 0.28 ≤ x
Ca ≤ 0.4 and green with 0.4 ≤ x
Ca. The crystal field parameter of octahedral Cr3+ 10Dq decreases strongly on increasing Ca-fraction from 17,850 cm−1 at x
Ca[8] = 0.020 to 16,580 cm−1 at x
Ca[8] = 0.745. The data could be fit with two model which do statistically not differ: (1) two linear functions with a discontinuity
close to x
Ca[8] ≈ 0.3,
7.
Titanite and rutile are a common mineral pair in eclogites, and many equilibria involving these phases are potentially useful in estimating pressures of metamorphism. We have reversed one such reaction,
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