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1.
Yu-Ran Luo 《Geochimica et cosmochimica acta》2004,68(4):691-699
Potentiometric measurements of Yttrium and Rare Earth Element (YREE) complexation by carbonate and bicarbonate indicate that the quality of carbonate complexation constants previously obtained via solvent exchange analyses are superior to characterizations obtained using solubility and adsorptive exchange analyses. The results of our analyses at 25°C are combined with the results of previous solvent exchange analyses to obtain YREE carbonate complexation constants over a wide range of ionic strength (0 ≤ I ≤3 molal). YREE carbonate complexation constants are reported for the following equilibria, M3++nHCO3−?M(CO3)n3−2n+nH+, where n = 1 or 2. Formation constants written in terms of HCO3− concentrations require only minor corrections for ion pairing relative to the corrections required for constants expressed in terms of CO32− concentrations. Formation constants for the above complexation equilibria, CO3Hβ1=[MCO3+][H+][M3+]−1[HCO3−]−1 and CO3Hβ2=[M(CO3)2−][H+]2[M3+]−1[HCO3−]−2, have very similar dependencies on ionic strength because the reaction MCO3++HCO3−?M(CO3)2−+H+ is isocoulombic. Potentiometric analyses indicate that the dependence of logCO3Hβ1 and logCO3Hβ2 on ionic strength at 25°C is given as
(A) 相似文献
2.
Ann D. Russell Bärbel Hönisch Howard J. Spero 《Geochimica et cosmochimica acta》2004,68(21):4347-4361
We investigate the sensitivity of U/Ca, Mg/Ca, and Sr/Ca to changes in seawater [CO32−] and temperature in calcite produced by the two planktonic foraminifera species, Orbulina universa and Globigerina bulloides, in laboratory culture experiments. Our results demonstrate that at constant temperature, U/Ca in O. universa decreases by 25 ± 7% per 100 μmol [CO32−] kg−1, as seawater [CO32−] increases from 110 to 470 μmol kg−1. Results from G. bulloides suggest a similar relationship, but U/Ca is consistently offset by ∼+40% at the same environmental [CO32−]. In O. universa, U/Ca is insensitive to temperature between 15°C and 25°C. Applying the O. universa relationship to three U/Ca records from a related species, Globigerinoides sacculifer, we estimate that Caribbean and tropical Atlantic [CO32−] was 110 ± 70 μmol kg−1 and 80 ± 40 μmol kg−1 higher, respectively, during the last glacial period relative to the Holocene. This result is consistent with estimates of the glacial-interglacial change in surface water [CO32−] based on both modeling and on boron isotope pH estimates. In settings where the addition of U by diagenetic processes is not a factor, down-core records of foraminiferal U/Ca have potential to provide information about changes in the ocean’s carbonate concentration.Below ambient pH (pH < 8.2), Mg/Ca decreased by 7 ± 5% (O. universa) to 16 ± 6% (G. bulloides) per 0.1 unit increase in pH. Above ambient pH, the change in Mg/Ca was not significant for either species. This result suggests that Mg/Ca-based paleotemperature estimates for the Quaternary, during which surface-ocean pH has been at or above modern levels, have not been biased by variations in surface-water pH. Sr/Ca increased linearly by 1.6 ± 0.4% per 0.1 unit increase in pH. Shell Mg/Ca increased exponentially with temperature in O. universa, where Mg/Ca = 0.85 exp (0.096*T), whereas the change in Sr/Ca with temperature was within the reproducibility of replicate measurements. 相似文献
3.
The soluble and insoluble hydrolysis products of palladium were investigated in aqueous solutions of 0.6 mol kg−1 NaCl at 298.2 K. Potentiometric titrations of millimolal palladium(II) solutions were used to monitor hydrolysis reactions of the mononuclear PdCl3OH2− and species. Spectrophotometric titrations were also used to corroborate the speciation change and to extract the correlative molar absorption coefficients for the PdCl3OH2− species in the 210-320 nm range. Longer-term potentiometric titrations systematically yielded precipitates which matured over a period of 6 weeks and resulted in a more extensive release of protons to the solution. Precipitation experiments in the 3-11 pH range showed the dominant precipitating phase to be Pd(OH)1.72Cl0.28. EXAFS measurements yielded an average of 3.50 O and 0.50 Cl atoms per Pd atom with a Pd-O distance of 2.012 Å and a Pd-Cl distance of 2.185 Å. Speciation modeling of proton and palladium mass balance data of experiments for palladium concentrations ranging from 0.047 to 10.0 mmol kg−1 required the presence of polynuclear complexes containing 3-9 palladium atoms. The existence of such complexes is moreover supported by previous investigations of palladium hydroxide chains of the type [Pd(OH)1.72Cl0.28]n, that are coiled and/or aggregated into nanometer-sized (15-40 Å) spheroids. 相似文献
4.
Melchor González-Davila 《Geochimica et cosmochimica acta》2005,69(1):83-93
The oxidation of Fe(II) with H2O2 at nanomolar levels in seawater have been studied using an UV-Vis spectrophotometric system equipped with a long liquid waveguide capillary flow cell. The effect of pH (6.5 to 8.2), H2O2 (7.2 × 10−8 M to 5.2 × 10−7 M), HCO3− (2.05 mM to 4.05 mM) and Fe(II) (5 nM to 500 nM) as a function of temperature (3 to 35 °C) on the oxidation of Fe(II) are presented. The oxidation rate is linearly related to the pH with a slope of 0.89 ± 0.01 independent of the concentration of HCO3−. A kinetic model for the reaction has been developed to consider the interactions of Fe(II) with the major ions in seawater. The model has been used to examine the effect of pH, concentrations of Fe(II), H2O2 and HCO3− as a function of temperature. FeOH+ is the most important contributing species to the overall rate of oxidation from pH 6 to pH 8. At a pH higher than 8, the Fe(OH)2 and Fe(CO3)22− species contribute over 20% to the rates. Model results show that when the concentration of O2 is two orders of magnitude higher than the concentration of H2O2, the oxidation with O2 also needs to be considered. The rate constants for the five most kinetically active species (Fe2+, FeOH+, Fe(OH)2, FeCO3, Fe(CO3)22−) in seawater as a function of temperature have been determined. The kinetic model is also valid in pure water with different concentrations of HCO3− and the conditions found in fresh waters. 相似文献
5.
M. Yamamoto 《Mineralium Deposita》1976,11(2):197-209
The pH and fO
2 dependences of the [Se2–]/[S2–] ratio in chloride solutions at 100°, 200° and 300°C are predicted thermodynamically. Under the high fO
2 conditions where sulfate species are dominant in solution, the [Se2–]/[S2–] ratio always increases with increasing pH and/or fO
2. Under the low fO
2 conditions where sulfide species are dominant in solution, the pH and fO
2 dependences of the [Se2–]/[S2–] ratio are seriously affected by the presence of native selenium. With native selenium present, the [Se2–]/[S2–] ratio decreases with increasing fO
2, but almost independent of pH in geologically important pH regions. When native selenium is absent, the [Se2–]/[S2–] ratio is solely a function of pH and independent of fO
2. Combining the above with the pH and fO
2 dependences of 34S value of aqueous sulfur species, we discuss the possible influences of the pH and fO
2 of ore-forming solutions on the relationship between the Se/S ratio and 34S value of hydrothermal sulfide minerals. The results are applied to some Japanese sulfide ore deposits. 相似文献
6.
Summary ?Results of experimental investigations in the dry system PtS-PdS-NiS at 1100°C, 1000°C, and 900°C are presented. The phases
observed at 1100°C are “cooperite” and a melt, at 1000°C “cooperite”, “braggite”, and a melt and at 900°C “cooperite”, “braggite”,
“vysotskite”, Ni1−xS, and a melt. At 1100°C the maximum solubility of Ni in ideal, Pd-free “cooperite” is 2.7 atomic per cent and the Pd-content
limit in Ni-free “cooperite” is 12.8 atomic per cent. At 1000°C the maximum solubility of Ni in ideal, Pd-free “cooperite”
is 3.3 atomic per cent and the Pd-content in Ni-free “cooperite” is 13.7 atomic per cent. The “braggite” composition ranges
from Pt0.56Pd0.38Ni0.06S and Pt0.59Pd0.41S in a Ni-saturated and Ni-free environment respectively to Pt0.18Pd0.80Ni0.02S and Pt0.14Pd0.86S respectively. At 900°C the maximum Ni-content in ideal Pd-free “cooperite” is 3.1 atomic per cent and the Pd-limit in Ni-free
“cooperite” is 12.5 atomic per cent. The “braggite” composition ranges from Pt0.59Pd0.29Ni0.12S and Pt0.60Pd0.40S for a Ni-saturated and Ni-free environment respectively, to Pd0.91Ni0.09S and PdS respectively. The Ni-content in “braggite” and “vysotskite” increases slightly with increasing Pt/Pd ratios and
is higher at 900°C than at 1000°C. Comparison of experimental trends with cooperite, braggite, and vysotskite analyses from
the literature implies high temperatures of formation for Pt-Pd-Ni sulphides in placers if Ni-saturation is assumed.
Received October 1, 1998;/revised version accepted September 7, 1999 相似文献
Zusammenfassung ?Synthetischer ,,Cooperit”, ,,Braggit” und “Vysotskit” im System PtS-PdS-NiS bei 1100°C, 1000°C und 900°C Ergebnisse experimenteller Untersuchungen im trockenen System PtS-PdS-NiS bei 1100°C, 1000°C und 900°C werden dargestellt. Bei 1100°C sind die Phasen “Cooperit” und Schmelze, bei 1000°C “Cooperit”, “Braggit” und Schmelze und bei 900°C “Cooperit”, “Braggit”, “Vysotskit”, Ni1−xS und Schmelze stabil. Bei 1100°C ist die maximale L?slichkeit von Ni in idealem, Pd-freiem “Cooperit” 2.7 Atomprozent und der Pd-Gehalt in Ni-freien “Cooperit” liegt bei maximal 12.8 Atomprozent. Bei 1000°C ist die maximale L?slichkeit von Ni in idealem, Pd-freien “Cooperit” 3.3 Atomprozent und der Pd-Gehalt in Ni-freien “Cooperit” liegt bei maximal 13.7 Atomprozent. Die Zusammensetzung des “Braggits” variiert zwischen Pt0.56Pd0.38Ni0.06S und Pt0.18Pd0.80Ni0.02S in einem Ni-ges?ttigtem und zwischen Pt0.59Pd0.41S und Pt0.14Pd0.86S in einem Ni-freien Umfeld. Bei 900°C liegt die maximale L?slichkeit von Ni in idealem Pd-freien “Cooperit” bei 3.1 Atomprozent und der Pd-Gehalt in Ni-freien “Cooperit” liegt bei maximal 12.5 Atomprozent. Die Zusammensetzung des “Braggits” variiert zwischen Pt0.59Pd0.29Ni0.12S und Pd0.89Ni0.08S in einem Ni-ges?ttigten und zwischen Pt0.59Pd0.40S und PdS in einem Ni-freien Umfeld. Der Nickelgehalt in “Braggit” und “Vysotskit” nimmt mit zunehmendem Pt/Pd Verh?ltnis zu und ist bei 900°C h?her als bei 1000°C. Ein Vergleich der experimentellen Trends mit Cooperit, Braggit und Vysotskit Analysen aus der Literatur weist auf eine Hochtemperaturbildung der Pt-Pd-Ni Sulfide in Seifenlagerst?tten hin, wenn man von Nickels?ttigung ausgeht.
Received October 1, 1998;/revised version accepted September 7, 1999 相似文献
7.
Instead of having been more or less constant, as once assumed, it is now apparent that the major ion chemistry of the oceans has varied substantially over time. For instance, independent lines of evidence suggest that calcium concentration ([Ca2+]) has approximately halved and magnesium concentration ([Mg2+]) approximately doubled over the last 100 million years. On the other hand, the calcite compensation depth, and hence the CaCO3 saturation, has varied little over the last 100 My as documented in deep sea sediments. We combine these pieces of evidence to develop a proxy for seawater carbonate ion concentration ([CO32−]) over this period of time. From the calcite saturation state (which is proportional to the product of [Ca2+] times [CO32−], but also affected by [Mg2+]), we can calculate seawater [CO32−]. Our results show that [CO32−] has nearly quadrupled since the Cretaceous. Furthermore, by combining our [CO32−] proxy with other carbonate system proxies, we provide calculations of the entire seawater carbonate system and atmospheric CO2. Based on this, reconstructed atmospheric CO2 is relatively low in the Miocene but high in the Eocene. Finally, we make a strong case that seawater pH has increased over the last 100 My. 相似文献
8.
Owen W Duckworth 《Geochimica et cosmochimica acta》2004,68(3):607-621
The dissolution of siderite (FeCO3) and rhodochrosite (MnCO3) under oxic and anoxic conditions is investigated at 298 K. The anoxic dissolution rate of siderite is 10−8.65 mol m−2 s−1 for 5.5 < pH < 12 and increases as [H+]0.75 for pH < 5.5. The pH dependence is consistent with parallel proton-promoted and water hydrolysis dissolution pathways. Atomic force microscopy (AFM) reveals a change in pit morphology from rhombohedral pits for pH > 4 to pits elongated at one vertex for pH < 4. Under oxic conditions the dissolution rate decreases to below the detection limit of 10−10 mol m−2 s−1 for 6.0 < pH < 10.3, and hillock precipitation preferential to steps is observed in concurrent AFM micrographs. X-ray photoelectron spectroscopy (XPS) and thermodynamic analysis identify the precipitate as ferrihydrite. At pH > 10.3, the oxic dissolution rate is as high as 10−7.5 mol m−2 s−1, which is greater than under the corresponding anoxic conditions. A fast electron transfer reaction between solution O2 or [Fe3+(OH)4]− species and surficial >FeII hydroxyl groups is hypothesized to explain the dissolution kinetics. AFM micrographs do not show precipitation under these conditions. Anoxic dissolution of rhodochrosite is physically observed as rhombohedral pit expansion for 3.7 < pH < 10.3 and is chemically explained by parallel proton- and water-promoted pathways. The dissolution rate law is 10−4.93[H+] + 10−8.45 mol m−2 s−1. For 5.8 < pH < 7.7 under oxic conditions, the AFM micrographs show a tabular precipitate growing by preferential expansion along the a-axis, though the macroscopic dissolution rate is apparently unaffected. For pH > 7.7 under oxic conditions, the dissolution rate decreases from 10−8.45 to 10−9.0 mol m−2 s−1. Flattened hillock precipitates grow across the entire surface without apparent morphological influence by the underlying rhodochrosite surface. XPS spectra and thermodynamic calculations implicate the precipitate as bixbyite for 5.8 < pH < 7.7 and MnOOH (possibly feitnkechtite) for pH >7.7. 相似文献
9.
Barry R. Bickmore Justin C. Wheeler Kathryn L. Nagy 《Geochimica et cosmochimica acta》2008,72(18):4521-4536
In light of recent work on the reactivity of specific sites on large (hydr)oxo-molecules and the evolution of surface topography during dissolution, we examined the ability to extract molecular-scale reaction pathways from macroscopic dissolution and surface charge measurements of powdered minerals using an approach that involved regression of multiple datasets and statistical graphical analysis of model fits. The test case (far-from-equilibrium quartz dissolution from 25 to 300 °C, pH 1-12, in solutions with [Na+] ? 0.5 M) avoids the objections to this goal raised in these recent studies. The strategy was used to assess several mechanistic rate laws, and was more powerful in distinguishing between models than the statistical approaches employed previously. The best-fit model included three mechanisms—two involving hydrolysis of Si centers by H2O next to neutral (>Si-OH0) and deprotonated (>Si-O−) silanol groups, and one involving hydrolysis of Si centers by OH−. The model rate law is
10.
Calculation of the UV-visible spectra and the stability of Mo and Re oxysulfides in aqueous solution
J.A. Tossell 《Geochimica et cosmochimica acta》2005,69(10):2497-2503
Erickson and Helz (2000) established that molybdate, MoO4−2, is quickly and completely transformed to thiomolybdate, MoS4−2, by reaction with sulfide. They monitored the equilibria and kinetics of this process by measuring the UV-visible spectra of solutions containing the different oxythiomolybdate species. There is interest in the analogous reactions for the ReO4− species but little experimental data. We have therefore calculated quantum-chemically the equilibrium constants in solution for the sulfidation reactions of both MoO4−2 and ReO4−, as well as recalculating their UV-visible charge-transfer spectra. Calculations using configuration interaction singles and time-dependent hybrid Hartree-Fock density functional methods give good absolute values and trends in UV-vis energies for both series. For MoO4−2 the calculated equilibrium constants for the various sulfidation steps match reasonably well against the experimental values (within two log K units). For the ReO4− sulfidation reaction the first two steps are considerably less favorable than for MoO4−2, suggesting that the “geochemical switch” of Erickson and Helz, a rapid transformation of oxyanion to thioanion highly dependent on sulfide concentration, will be less effective in the Re case. However, both our calculations and experiment indicate that ReO4− and ReS4− are both easier to reduce than their Mo analogs, so that reduction of these Re(VII) species will be the preferred mechanism for their removal from seawater. A previous suggestion that the neutral species MoO4H2 is actually the hydrated octahedral Mo(OH)6 species is found to be incorrect, but the MoO3(OH2)3 species, a highly distorted six-coordinate complex, is almost competitive in energy with MoO4H2 plus two H2O. 相似文献
11.
Secular variation in the major-ion chemistry of seawater: Evidence from fluid inclusions in Cretaceous halites 总被引：5，自引：0，他引：5
The major-ion (Mg2+, Ca2+, Na+, K+, , and Cl−) chemistry of Cretaceous seawater was determined from analyses of seawater-derived brines preserved as fluid inclusions in marine halites. Fluid inclusions in primary halite from three evaporite deposits were analyzed by the environmental scanning electron microscopy (ESEM) X-ray energy dispersive spectrometry (EDS) technique: the Early Cretaceous (Aptian, 121.0-112.2 Ma) of the Sergipe basin, Brazil and the Congo basin, Republic of the Congo, and the Early to Late Cretaceous (Albian to Cenomanian, 112.2-93.5 Ma) of the Khorat Plateau, Laos, and Thailand. The fluid inclusions in halite indicate that Cretaceous seawater was enriched several fold in Ca2+, depleted in , Na+, and Mg2+, and had lower Na+/Cl−, Mg2+/Ca2+, and Mg2+/K+ ratios compared to modern seawater. Elevated Ca2+ concentrations, with Ca2+ > at the point of gypsum saturation, allowed Cretaceous seawater to evolve into Mg2+-Ca2+-Na+-K+-Cl− brines lacking measurable .The major-ion composition of Cretaceous seawater was modeled from fluid inclusion chemistries for the Aptian and the Albian-Cenomanian. Aptian seawater was extreme in its Ca2+ enrichment, more than three times higher than present day seawater, with a Mg2+/Ca2+ ratio of 1.1-1.3. Younger, Albian-Cenomanian seawater had lower Ca2+ concentrations, and a higher Mg2+/Ca2+ ratio of 1.2-1.7. Cretaceous (Aptian) seawater has the lowest Mg2+/Ca2+ ratios so far documented in Phanerozoic seawater from fluid inclusions in halite, and within the range chemically favorable for precipitation of low-Mg calcite ooids and cements. Results from halite fluid inclusions, together with Mg2+/Ca2+ ratios measured from echinoderm and rudist calcite, all indicate that Early Cretaceous seawater (Hauterivian, Barremian, Aptian, and Albian) had lower Mg2+/Ca2+ ratios than Late Cretaceous seawater (Coniacian, Santonian, and Campanian). Low Aptian-Albian Mg2+/Ca2+ seawater ratios coincide with negative excursions of 87Sr/86Sr ratios and δ34SSO4, and peak Cretaceous ocean crust production rates, all of which suggests a link between seawater chemistry and midocean ridge hydrothermal brine flux. 相似文献
12.
Alfonso Mucci 《Aquatic Geochemistry》2004,10(1-2):139-169
The dissolution behavior of natural, ordered kutnahorite (Mn1.14Ca0.82Mg0.04Fe0.012(CO3)2) and a disordered, calcian rhodochrosite (Mn1.16Ca0.78Mg0.06(CO3)2) precipitated in the laboratory was investigated in deionized distilled water and artificial seawater in both open and closed systems at 25 °C, one atmosphere total pressure, and various pCO2s. Both solids dissolved congruently in distilled water in an open system and yielded identical long-term equilibration or extrapolated ion activity products, IAPpkt = aCa 2+aMn 2+(aCO 3 2?)2 = 1.7 (±0.12)× 10?21 or pIAPpkt = 20.77 (±0.03). This value is believed to be the thermodynamic solubility product of pseudokutnahorite. In contrast, the steady state ion concentration products, ICPpkt = [Ca2+][Mn2+][CO3 2?]2, measured following the dissolution of both minerals in artificial seawater increase as the CO2 partial pressure decreases and the [Mn2+]:[Ca2+] ratio increases. These observations are interpreted as resulting from the formation of phases of different stoichiometry in response to large variations of the [Mn2+]:[Ca2+] ratio in solution. These data and results of calcite-seawater equilibration experiments in the presence of various dissolved Mn(II) concentrations define the fields of stability of manganoan calcites and calcian rhodochrosites in seawater within Lippmann phase diagrams for the CaCO3–MnCO3–H2O system. Results of this study reveal that the nature (i.e., mineralogy) and composition of manganese-rich carbonate phases that may form under suboxic/anoxic conditions in marine sediments are dictated by the porewater [Mn2+]:[Ca2+] ratio, the abundance of calcite surfaces and reaction kinetics. 相似文献
13.
The mobility and transport of gold in low-temperature waters and brines is affected by the aqueous speciation of gold, which is sensitive in particular to pH, oxidation and halide concentrations. In this study, we use UV-Vis spectrophotometry to identify and measure the thermodynamic properties of Au(III) aqueous complexes with chloride, bromide and hydroxide. Au(III) forms stable square planar complexes with hydroxide and halide ligands. Based on systematic changes in the absorption spectra of solutions in three binary systems NaCl-NaBr, NaCl-NaOH and NaBr-NaOH at 25 °C, we derived log dissociation constants for the following mixed and end-member halide and hydroxide complexes: [AuCl3Br]−, [AuCl2Br2]−, [AuBr3Cl]− and [AuBr4]−; [AuCl3(OH)]−, [AuCl2(OH)2]−, [AuCl(OH)3]− and [Au(OH)4]−; and [AuBr3(OH)]−, [AuBr2(OH)2]− and [AuBr(OH)3]−. These are the first reported results for the mixed chloride-bromide complexes. Increasing temperature to 80 °C resulted in an increase in the stability of the mixed chloride-bromide complexes, relative to the end-member chloride and bromide complexes. For the [AuCl(4−n)(OH)n]− series of complexes (n = 0-4), there is an excellent agreement between our spectrophotometric results and previous electrochemical results of Chateau et al. [Chateau et al. (1966)]. In other experiments, the iodide ion (I−) was found to be unstable in the presence of Au(III), oxidizing rapidly to I2(g) and causing Au to precipitate. Predicted Au(III) speciation indicates that Au(III) chloride-bromide complexes can be important in transporting gold in brines with high bromide-chloride ratios (e.g., >0.05), under oxidizing (atmospheric), acidic (pH < 5) conditions. Native gold solubility under atmospheric oxygen conditions is predicted to increase with decreasing pH in acidic conditions, increasing pH in alkaline conditions, increasing chloride, especially at acid pH, and increasing bromide for bromide/chloride ratios greater than 0.05. The results of our study increase the understanding of gold aqueous geochemistry, with the potential to lead to new methods for mineral exploration, hydrometallurgy and medicine. 相似文献
14.
By using a specially designed and constructed isopiestic apparatus, we measured the osmotic coefficients at 313.2 K for the NaOH-NaAl(OH)4-H2O system with the total alkali molality, mNaOHT (mNaOH + mNaAl[OH]4), from 0.05 mol/kg H2O to 12 mol/kg H2O and αK (mNaOHT/mNaAl(OH)4) from 1.64 to 5.53. The mean standard deviation of the measurements is 0.0038. Several sets of the Pitzer model parameters for NaOH-NaAl(OH)4-H2O system were then obtained by regressing the measured osmotic coefficients with the Pitzer model and the Pitzer model parameters for NaOH(aq). One set of the results is as follows: β(0)NaOH: 0.08669, β(1)NaOH: 0.31446, β(2)NaOH: −0.00007367, CΦNaOH: 0.003180, β(0)NaAl(OH)4: 0.03507, β(1)NaAl(OH)4: 0.02401, CΦNaAl(OH)4: −0.001066, θOH−Al(OH)4−: 0.08177, ΨNa+OH−Al(OH)4−: −0.01162. The mean standard difference between the calculated and the measured osmotic coefficients is 0.0088. With the obtained Pitzer model parameters, we calculated the values of K = (γNaAl(OH)4,cal2 · mAl(OH)4−,exp)/(γNaOH,cal2 · mOH−,exp) for the gibbsite solubility. The results show that the obtained Pitzer model parameters are reliable, and the relative error of the calculated activity coefficients should be < 2.1%. We also compared the calculated gibbsite solubility data among several activity coefficients models over a range of mNaOHT at various temperatures. The comparison indicates that our activity coefficients model may be approximately applied in the ranges of temperature from 298.2 to 323.2 K and mNaOHT from 0 to 8 mol/kg H2O. We also calculated the stoichiometric activity coefficients of NaOH and NaAl(OH)4 and the activity of H2O for the NaOH-NaAl(OH)4-H2O system, and these calculations establish their variations with mNaOHT and αK. These variations imply that the strengths of the repulsive interactions among various anions are in the following sequence: Al(OH)4−-Al(OH)4− < Al(OH)4−-OH− < OH−-OH−, and the attractive interaction between Al(OH)4− and H2O is weaker than that between OH− and H2O. 相似文献
15.
Summary The complexation of aluminium(III) and silicon(IV) was studied in a simplified seawater medium (0.6 M Na(Cl)) at 25 °C. The
measurements were performed as potentiometric titrations using a hydrogen electrode with OH
− ions being generated coulometrically. The total concentrations of Si(IV) and Al(III) respectively [Si
tot
] and [Al
t
ot], and −log[H
+] were varied within the limits 0.3 < [Si
tot
] < 2.5 mM, 0.5 < [Al
tot
] < 2.6 mM, and 2 ≤ -log[H
+] ≤ 4.2. Within these ranges of concentration, evidence is given for the formation of an AlSiO(OH)
3
2+
complex with a formation constant log β1,1-1 = −2.75 ± 0.1 defined by the reaction
Al
3++Si (OH)4 ↔ AlOSi(OH)
3
2+
+H
+
An extrapolation of this value to I=0 gives log β1,1-1 = −2.30. The calculated value of log K (Al
3++SiO(OH)
3
−
↔ AlOSi(OH)
3
2+
) = 6.72 (I=0.6 M) can be compared with corresponding constants for the formation of AlF
2+ and AlOH
2+ , which are equal to 6.16 and 8.20. Obviously, the stability of these Al(III) complexes decreases within the series OH
−>SiO(OH)
3
−
> F
− 相似文献
16.
The major-ion composition of Permian seawater 总被引：1，自引：0，他引：1
Tim K. Lowenstein Michael N. Timofeeff Juske Horita 《Geochimica et cosmochimica acta》2005,69(7):1701-1719
The major-ion (Mg2+, Ca2+, Na+, K+, SO42−, and Cl−) composition of Permian seawater was determined from chemical analyses of fluid inclusions in marine halites. New data from the Upper Permian San Andres Formation of Texas (274-272 Ma) and Salado Formation of New Mexico (251 Ma), analyzed by the environmental scanning electron microscopy (ESEM) X-ray energy-dispersive spectrometry (EDS) method, along with published chemical compositions of fluid inclusions in Permian marine halites from North America (two formations of different ages) and the Central and Eastern European basins (eight formations of four different ages) show that Permian seawater shares chemical characteristics with modern seawater, including SO42− > Ca2+ at the point of gypsum precipitation, evolution into Mg2+-Na+-K+-SO42−-Cl− brines, and Mg2+/K+ ratios ∼5. Permian seawater, however, is slightly depleted in SO42− and enriched in Ca2+, although modeling results do not rule out Ca2+ concentrations close to those in present-day seawater. Na+ and Mg2+ in Permian seawater are close to (slightly below) their concentrations in modern seawater. Permian and modern seawater are both classified as aragonite seas, with Mg2+/Ca2+ ratios >2, conditions favorable for precipitation of aragonite and magnesian calcite as ooids and cements.The chemistry of Permian seawater was modeled using the chemical composition of brine inclusions for three periods: Lower Permian Asselian-Sakmarian (296-283 Ma), Lower Permian Artinskian-Kungurian (283-274 Ma), and Upper Permian Tatarian (258-251 Ma). Parallel changes in the chemistry of brine inclusions from equivalent age evaporites in North America, Central Europe, and Eastern Europe show that seawater underwent secular variations in chemistry over the 50 million years of the Permian. Modeled SO42− concentrations are 20 mmol per kg H2O (mmolal) and 19 mmolal in the Asselian-Sakmarian and Artinskian-Kungurian, with higher concentrations in the Upper Permian Tatarian (23 mmolal). Modeled Ca2+ is at or above its concentration in modern seawater throughout the Permian. Mg2+ is close to (slightly below) its concentration in modern seawater (55 mmolal) in the Asselian-Sakmarian (52 mmolal), and Tatarian (52 mmolal), but slightly higher than modern seawater in the Artinskian-Kungurian (60 mmolal). Mg2+/Ca2+ ratios are 3.5 (total range = 2.7 to 5.5) in the Lower Permian and rose slightly to 3.7 (total range = 3.1 to 5.8) in the Upper Permian, primarily due to decreases in Ca2+. These results are consistent with models that predict oscillations in the major-ion composition of Phanerozoic seawater on the basis of changes in the midocean ridge/river water flux ratio driven by changes in the rate of midocean ridge crust production.The Permian was characterized by low sea levels, icehouse conditions, and southern hemisphere glaciation. Such conditions, analogous to the present ice age, and the similarities between Permian seawater and modern seawater, all suggest that general Phanerozoic supercycles, driven by mantle convection and global volcanicity, also control the major-ion chemistry of seawater. 相似文献
17.
A. Y. Barkov R. F. Martin M. E. Fleet G. T. Nixon V. M. Levson 《Mineralogy and Petrology》2008,92(1-2):9-29
Summary We have conducted electron microprobe (EMP) analysis of 158 grains of platinum-group minerals (PGM; 0.1–1 mm in size) from
11 placer samples collected from Holocene fluvial placers and buried paleochannel placers at various localities in British
Columbia. These grains principally comprise Pt-Fe-(Cu) alloy minerals: Fe-rich platinum [ΣPGE:(Fe + Cu + Ni) = 3.6–7.6], Pt3Fe-type alloy (isoferroplatinum or Fe-rich platinum), subordinate “Pt2Fe”-type alloy (probably, a compositional variant of Fe-rich platinum) and the tulameenite-tetraferroplatinum series. Less-abundant
are iridium [Ir-dominant Ir-Os-(Pt) alloy] and osmium [Os-dominant Os-Ir-(Pt) alloy]. Ruthenium [Ru-dominant Ru-Ir-Os alloy]
occurs as a single grain. One of these Pt-Fe alloy grains is unusually zoned; its core zone is: Pt74.0Fe20.4Cu1.9Ir1.5Rh1.1Pd1.0Os0.08Ru0.01Ni0.01 (in at%) [ΣPGE:(Fe + Cu + Ni) = 3.5], and its rim zone is: Pt78.5Fe15.5Cu1.7Ir1.5Rh1.4 Pd1.2Ni0.15Os0.06Ru<0.01 [ΣPGE:(Fe + Cu + Ni) = 4.8]. This zoning indicates late-stage removal of Fe and corresponding addition of Pt, probably as
a result of interaction with a late fluid phase. Various combinations of minor elements: Ir-Rh, Rh-Pd, and Ir-Rh-Pd are observed
in the analysed Pt-Fe-Cu alloys. However, the Ir-Pd pair appears to be prohibited because of crystallochemical factors. Minute
PGM inclusions in Pt-Fe alloy grains, likely derived from the Tulameen complex, comprise: hongshiite (Pt1.04Pd0.02 Cu0.93), sperrylite (Pt0.93Ir0.03)Σ0.96(As2.02Sb0.01)Σ2.03, hollingworthite-platarsite (Rh0.74 Pt0.21Fe0.02Pd0.02Ir0.01)Σ1.00S0.91As1.10, cuprorhodsite-malanite (Cu0.91Fe0.03Ni<0.01)Σ0.95 (Rh1.06Pt0.89Ir<0.01)Σ1.95S4.10, a rare Te-rich isomertieite (Pd10.96Fe0.03)Σ10.99(Sb1.13 Te0.94)Σ2.07As1.93, and an unusual Pt-Pd-Rh antimonide [(Pt + Pd + Rh):(Sb + As) = 1.2–1.25], related to genkinite. This antimonide may exhibit
a minor solid solution extending from genkinite toward stumpflite. In addition, 20 grains of diopside [Ca46.4–49.1Mg42.8–48.2Fe3.1–8.1; ≤0.59 wt% Cr2O3] and 20 grains of olivine [Fo86.8–91.5 Fa7.9–12.5], from a PGM-bearing placer located in the vicinity of the Tulameen complex, were analysed. The compositional ranges of these
placer silicates are comparable to those of clinopyroxene and olivine in the olivine clinopyroxenite and dunite units of the
Tulameen complex. The majority of the analysed placer PGM grains were probably derived from Alaskan-type source rocks, whereas
an ophiolitic source, associated with the Atlin ophiolite complex, is suggested for the placer PGM deposits in the Atlin area,
northern British Columbia.
Authors’ addresses: Andrei Y. Barkov, Robert F. Martin, Department of Earth and Planetary Sciences, McGill University, 3450 University Street, Montreal, Quebec H3A 2A7, Canada;
Michael E. Fleet, Department of Earth Sciences, University of Western Ontario, London, Ontario, N6A 5B7, Canada; Graham T. Nixon and Victor M. Levson, B.C. Geological Survey, Ministry of Energy, Mines and Petroleum Resources, PO Box 9320 Stn. Prov. Govt., Victoria, British
Columbia V8W 9N3, Canada 相似文献
18.
Marine organisms must possess strategies enabling them to initiate calcite precipitation despite the unfavorable conditions for inorganic precipitation in surface seawater. These strategies are poorly understood. Here we compare two potential strategies of marine calcifyers to manipulate seawater chemistry in order to initiate calcite precipitation: Removal of Mg2+ and H+ ions from seawater solutions. An experimental setup was used to monitor the onset of inorganic precipitation on seed crystals as a function of the Mg2+ concentration and pH in artificial seawater. We focused on precipitation rates typical for biogenic calcification in planktonic foraminifera (∼10−3 mol m−2 h−1) and time scales typical for the initiation of calcification in these organisms (minutes to hours). We find that the carbonate ion concentration has to increase by a factor of ∼13 when [Mg2+] increases from 0 to 53 mmol kg−1 in order to maintain a typical biogenic precipitation rate. Model calculations for the energy requirement for various scenarios of Mg2+ and H+ removal including Ca2+ exchange and CO2 diffusion are presented. We conclude that the more cost-effective strategy to initiate calcite precipitation in foraminifera is H+ removal, rather than Mg2+ removal. 相似文献
19.
Distribution coefficients were obtained for yttrium and the rare earth elements (YREEs) in aqueous solutions containing freshly precipitated hydroxides of trivalent cations (Fe3+, Al3+, Ga3+, and In3+). Observed patterns of log i K S–, where i K S = [MS i ][M3+]?1[S i ]?1, [MS i ] is the concentration of a sorbed YREE, [M3+] is the concentration of a free hydrated YREE ion, and [S i] is the concentration of a sorptive solid substrate (Fe(III), Al, Ga, In)– exhibited similarities to patterns of YREE solution complexation constants with hydroxide (OH β 1) and fluoride (F β 1), but also distinct differences. The log i K S pattern for YREE sorption on Al hydroxide precipitates is very similar to the pattern of YREE hydroxide stability constants (logOH β 1) in solution. Linear free-energy relationships between log i K S and logOH β 1 showed excellent correlation for YREE sorption on Al hydroxide precipitates, good correlation for YREE sorption on Ga or In hydroxide precipitates, yet poor correlation for YREE sorption on Fe(III) hydroxide precipitates. Whereas the correlation between log i K S and logF β 1 was generally poor, patterns of log( i K S/F β 1) displayed substantially increased smoothness compared to patterns of log i K S. This indicates that the conspicuous sequence of inflections along the YREE series in the patterns of log i K S and logF β 1 is very similar, particularly for In and Fe(III) hydroxide precipitates. While the log i K S patterns obtained with Fe(III) hydroxide precipitates in this work are quite distinct from those obtained with Al, Ga, and In hydroxide precipitates, they are in good agreement with patterns of YREE sorption on ferric oxyhydroxide precipitates reported by others. Furthermore, our log i K S patterns for Fe(III) hydroxide precipitates bear a striking resemblance to predicted log i K S patterns for natural surfaces that are based on YREE solution chemistry and shale-normalized YREE concentrations in seawater. Yttrium exhibits an itinerant behavior among the REEs: sorption of Y on Fe(III) hydroxide precipitates is intermediate to that of La and Ce, while for Al hydroxide precipitates Y sorption is similar to that of Eu. This behavior of Y can be rationalized from the propensities of different YREEs for covalent vs. ionic interactions. The relatively high shale-normalized concentration of Y in seawater can be explained in terms of primarily covalent YREE interactions with scavenging particulate matter, whereby Y behaves as a light REE, and primarily ionic interactions with solution ligands, whereby Y behaves as a heavy REE. 相似文献
20.
An atomic force microscopy study of calcite dissolution in saline solutions: The role of magnesium ions 总被引：1，自引：0，他引：1
In situ Atomic Force Microscopy, AFM, experiments have been carried out using calcite cleavage surfaces in contact with solutions of MgSO4, MgCl2, Na2SO4 and NaCl in order to attempt to understand the role of Mg2+ during calcite dissolution. Although previous work has indicated that magnesium inhibits calcite dissolution, quantitative AFM analyses show that despite the fact that Mg2+ inhibits etch pit spreading, it increases the density and depth of etch pits nucleated on calcite surfaces and, subsequently, the overall dissolution rates: i.e., from 10−11.75 mol cm−2 s−1 (in deionized water) up to 10−10.54 mol cm−2 s−1 (in 2.8 M MgSO4). Such an effect is concentration-dependent and it is most evident in concentrated solutions ([Mg2+] >> 50 mM). These results show that common soluble salts (especially Mg sulfates) may play a critical role in the chemical weathering of carbonate rocks in nature as well as in the decay of carbonate stone in buildings and statuary. 相似文献