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1.
The diffusivity of oxygen was determined in melts of Jadeite (NaAlSi2O6) and diopside (CaMgSi2O6) compositions using diffusion couples with 18O as a tracer. In the Jadeite melt, the diffusivity of oxygen increases from 6.87?0.25+0.28 × 10?10cm2/sec at 5 Kb to 1.32 ± 0.08 × 10?9cm2/sec at 20 Kb at constant temperature (1400°C), whereas in the diopside melt at 1650°C, the diffusivity decreases from 7.30?0.180.29 × 10?7cm2/sec at 10 Kb to 5.28?0.55+0.60 × 10?7cm2/sec at 17 Kb. These results demonstrate that the diffusivity is inversely correlated with the viscosity of the melt. For the jadeite melt, in particular, the inverse correlation is very well approximated by the Eyring equation using the diameter of oxygen ions as a unit distance of translation, suggesting that the viscous flow is rate-limited by the diffusion of individual oxygen ions. In the diopside melt, the activation volume is slightly greater than the molar volume of oxygen ion, indicating that the individual oxygen ion is the diffusion unit. The negative activation volume obtained for the jadeite melt is interpreted as the volume decrease associated with a diffusive jump of an oxygen ion due to local collapse of the network structure.  相似文献   

2.
The 3He4He ratios measured in 27 Southern Africa diamond stones, four from Premier Mine and the rest of unidentified origin, range from 4.2 × 10?8 to 3.2 × 10?4, with three stones above 1 × 10?4. We conclude that the initial helium isotopic ratio (3He4He)0 in the earth was significantly higher than that of the planetary helium-A (3He4He = 1.42 × 10?4), but close to the solar helium (3He4He ? 4 × 10?4).The apparent K-Ar ages for the twelve diamonds of unidentified origin show enormously old age, indicating excess argon-40. 3He4He evolution in diamonds suggests that the diamonds with the high 3He4He ratio (>2 × 10?4) may be as old as the earth.Noble gas elemental abundance in the diamonds relative to the air noble gas abundance shows monotonie decrease with a decreasing mass number.This paper discusses the implications of these observations on the early solar system and the origin of diamonds.  相似文献   

3.
Cyclic voltammetry has been done for Ni2+, Co2+, and Zn2+ in melts of diopside composition in the temperature range 1425 to 1575°C. Voltammetric curves for all three ions excellently match theoretical curves for uncomplicated, reversible charge transfer at the Pt electrode. This implies that the neutral metal atoms remain dissolved in the melt. The reference electrode is a form of oxygen electrode. Relative to that reference assigned a reduction potential of 0.00 volt, the values of standard reduction potential for the ions are E1 (Ni2+Ni0, diopside, 1500°C) = ?0.32 ± .01 V, E1 (Co2+Co0, diopside, 1500°C) = ?0.45 ± .02 V, and E1 (Zn2+Zn0, diopside, 1500°C) = ?0.53 ± .01 V. The electrode reactions are rapid, with first order rate constants of the order of 10?2 cm/sec. Diffusion coefficients were found to be 2.6 × 10?6 cm2/sec for Ni2+, 3.4 × 10?6 cm2/sec for Co2+, and 3.8 × 10?6 cm2/sec for Zn2+ at 1500°C. The value of E1 (Ni2+Ni0, diopside) is a linear function of temperature over the range studied, with values of ?0.35 V at 1425°C and ?0.29 V at 1575°C. At constant temperature the value of E1 (Ni2+Ni0, 1525°C) was not observed to vary with composition over the range CaO · MgO · 2SiO2 to CaO·MgO·3SiO2 or from 1.67 CaO·0.33MgO·2SiO2 to 0.5 CaO·1.5MgO·2SiO2. The value for the diffusion coefficient for Ni2+ decreased by an order of magnitude at 1525°C over the compositional range CaO · MgO · 1.25SiO2 to CaO · MgO · 3SiO2. This is consistent with a mechanism by which Ni2+ ions diffuse by moving from one octahedral coordination site to another in the melt, with the same Ni2+ species discharging at the cathode regardless of the SiO2 concentration in the melt.  相似文献   

4.
Xanthates are used in the flotation of sulfide ores although their aqueous solutions are not stable under certain conditions. Their stability in acidic and weakly acidic aqueous solutions was therefore investigated, as these media are required for some processes.The peak absorbances of ethylxanthate ion and carbon disulfide were first determined in aqueous solution. The decomposition of ethylxanthate ion was analyzed by measuring variations in absorbance (at 301 nm) and pH with respect to time. A pH regulation system was then used while measuring variations in absorbance and productions of protons caused by xanthate decomposition.The results concerning xanthate half-lives show good agreement with the literature, but the kinetic results deviate substantially. The following relation was obtained for half-life:
T12=9.67×10?6(pH)11;4?7;T12in seconds
We established that ethylxanthate decomposition at pH 4 is a first order reaction with respect to ethylxanthate concentration, and postulating this order to the other pH values, the following kinetic relation was found:
v= ?(1.22×104[H+]?1.36×10?2)([EtX?]) (4?pH?7)
where v is the rate of decomposition (mol l?1 min?1), and [EtX?] is the ethylxanthate concentration when the decomposition equilibria are reached (mol l?1). The better concentration was found to obey the law:
[EtX?]=3.142×10?5 pH ? 1.255 × 10?4 (4?pH?6)
  相似文献   

5.
The decay constant 87Rb has been redetermined by measuring the amount of radiogenic 87Sr produced over a period of 19 years, in 20 g samples of purified RbClO4, using isotope dilution techniques. The rubidium sample was spiked with 84Sr and the nanogram quantities of strontium separated by coprecipitation with Ba(NO3)2. Analyses were carried out on a 25cm, 90° sector mass spectrometer equipped with a Spiraltron electron multiplier. Measurement of three independent ratios permitted continuous monitoring of the ion beam fractionation. The average of nine determinations gives a value for the decay constant of 1.419(±0.012) × 10?11 yr?1 (2σ). [τ12 = 4.89(±0.04) × 1010yr.]  相似文献   

6.
Solution calorimetric measurements compared with solubility determinations from the literature for the same samples of gibbsite have provided a direct thermochemical cycle through which the Gibbs free energy of formation of [Al(OH)4 aq?] can be determined. The Gibbs free energy of formation of [Al(OH)4 aq?] at 298.15 K is ?1305 ± 1 kJ/mol. These heat-of-solution results show no significant difference in the thermodynamic properties of gibbsite particles in the range from 50 to 0.05 μm.The Gibbs free energies of formation at 298.15 K and 1 bar pressure of diaspore, boehmite and bayerite are ?9210 ± 5.0, ?918.4 ± 2.1 and ?1153 ± 2 kJ/mol based upon the Gibbs free energy of [A1(OH)4 aq?] calculated in this paper and the acceptance of ?1582.2 ± 1.3 and ?1154.9 ± 1.2 kJ/mol for the Gibbs free energy of formation of corundum and gibbsite, respectively.Values for the Gibbs free energy formation of [Al(OH)2 aq+] and [AlO2 aq?] were also calculated as ?914.2 ± 2.1 and ?830.9 ± 2.1 kJ/mol, respectively. The use of [AlC2 aq?] as a chemical species is discouraged.A revised Gibbs free energy of formation for [H4SiO4aq0] was recalculated from calorimetric data yielding a value of ?1307.5 ± 1.7 kJ/mol which is in good agreement with the results obtained from several solubility studies.Smoothed values for the thermodynamic functions CP0, (HT0 - H2980)T, (GT0 - H2980)T, ST0 - S00, ΔH?,2980 kaolinite are listed at integral temperatures between 298.15 and 800 K. The heat capacity of kaolinite at temperatures between 250 and 800 K may be calculated from the following equation: CP0 = 1430.26 ? 0.78850 T + 3.0340 × 10?4T2 ?1.85158 × 10?4T212 + 8.3341 × 106 T?2.The thermodynamic properties of most of the geologically important Al-bearing phases have been referenced to the same reference state for Al, namely gibbsite.  相似文献   

7.
Silver in the metal phases of Cape York (IIIA) and Grant (IIIB) has been determined after an extensive surface cleaning process. The 107Ag109Ag was found to be enriched over that found in terrestrial Ag by ~7%. to 19%., demonstrating the presence of excess 107Ag (107Ag1) in this class of meteorites. An effort was made to find schreibersite with a distinctive 108Pd/109Ag ratio in order to establish a three-point isochron, but the results are not markedly different from those obtained for the bulk metal. The Ag isotopic ratio of sulfides from the same meteorites were nearly normal in composition. These results demonstrate correlations of 107Ag109Ag with 108Pd109Ag between coexisting phases of two iron meteorites that are associated with planetary differentiation processes. The ratios 107Ag1108Pd were found to be 1.7 × 10?5 and 1.2 × 10?5 for Cape York and Grant, respectively. These observations are in support of the widespread presence of 107Pd in the early solar system. The difference in isotopic composition between metal and sulfide phases demonstrates that silver diffusion was small (over 6.5 × 106 y) indicating a cooling rate much greater than 150°C/my for meteorites which have been attributed to small planetary cores. Uranium determinations were carried out on the metal phases and concentrations of ~ 1 × 10 12 g U/g and 2 × 10?10g U/g were found for Cape York and Grant, respectively. The Pb in these meteorites was determined using the improved cleaning procedures and chemical separations with low blank levels. The results confirm the presence of variable proportions of radiogenic Pb in both the metal and sulfide phases of iron meteorites. No simple explanation for the presence of radiogenic lead is apparent; while terrestrial contamination may appear to be the obvious explanation, it is possible that this effect could result from relatively recent metamorphism in the meteorite parent body.  相似文献   

8.
Solubility curves were determined for a synthetic gibbsite and a natural gibbsite (Minas Gerais, Brazil) from pH 4 to 9, in 0.2% gibbsite suspensions in 0.01 M NaNO3 that were buffered by low concentrations of non-complexing buffer agents. Equilibrium solubility was approached from oversaturation (in suspensions spiked with Al(NO3)3 solution), and also from undersaturation in some synthetic gibbsite suspensions. Mononuclear Al ion concentrations and pH values were periodically determined. Within 1 month or less, data from over-and undersaturated suspensions of synthetic gibbsite converged to describe an equilibrium solubility curve. A downward shift of the solubility curve, beginning at pH 6.7, indicates that a phase more stable than gibbsite controls Al solubility in alkaline systems. Extrapolation of the initial portion of the high-pH side of the synthetic gibbsite solubility curve provides the first unified equilibrium experimental model of Al ion speciation in waters from pH 4 to 9.The significant mononuclear ion species at equilibrium with gibbsite are Al3+, AlOH2+, Al(OH)+2 and Al(OH)?4, and their ion activity products are 1K50 = 1.29 × 108, 1Ks1 = 1.33 × 103, 1Ks2 = 9.49 × 10?3 and 1Ks4 = 8.94 × 10?15. The calculated standard Gibbs free energies of formation (ΔG°f) for the synthetic gibbsite and the A1OH2+, Al(OH)+2 and Al(OH)?4 ions are ?276.0, ?166.9, ?216.5 and ?313.5 kcal mol?1, respectively. These ΔG°f values are based on the recently revised ΔG°f value for Al3+ (?117.0 ± 0.3 kcal mol?1) and carry the same uncertainty. The ΔG°f of the natural gibbsite is ?275.1 ± 0.4 kcal mol?, which suggests that a range of ΔG°f values can exist even for relatively simple natural minerals.  相似文献   

9.
The relative reactivities of pulverized samples (100–200 mesh) of 3 marcasite and 7 pyrite specimens from various sources were determined at 25°C and pH 2.0 in ferric chloride solutions with initial ferric iron concentrations of 10?3 molal. The rate of the reaction:
FeS2 + 14Fe3+ + 8H2O = 15Fe2+ + 2SO2?4 + 16H+
was determined by calculating the rate of reduction of aqueous ferric ion from measured oxidation-reduction potentials. The reaction follows the rate law:
?dmFe3+dt = k(AM)mFe3+
where mFe3+ is the molal concentration of uncomplexed ferric iron, k is the rate constant and AM is the surface area of reacting solid to mass of solution ratio. The measured rate constants, k, range from 1.0 × 10?4 to 2.7 × 10?4 sec?1 ± 5%, with lower-temperature/early diagenetic pyrite having the smallest rate constants, marcasite intermediate, and pyrite of higher-temperature hydrothermal and metamorphic origin having the greatest rate constants. Geologically, these small relative differences between the rate constants are not significant, so the fundamental reactivities of marcasite and pyrite are not appreciably different.The activation energy of the reaction for a hydrothermal pyrite in the temperature interval of 25 to 50°C is 92 kJ mol?1. This relatively high activation energy indicates that a surface reaction controls the rate over this temperature range. The BET-measured specific surface area for lower-temperature/early diagenetic pyrite is an order of magnitude greater than that for pyrite of higher-temperature origin. Consequently, since the lower-temperature types have a much greater AM ratio, they appear to be more reactive per unit mass than the higher temperature types.  相似文献   

10.
Small live individuals of Globigerinoides sacculifer which were cultured in the laboratory reached maturity and produced garnets. Fifty to ninety percent of their skeleton weight was deposited under controlled water temperature (14° to 30°C) and water isotopic composition, and a correction was made to account for the isotopic composition of the original skeleton using control groups.Comparison of. the actual growth temperatures with the calculated temperature based on paleotemperature equations for inorganic CaCO3 indicate that the foraminifera precipitate their CaCO3 in isotopic equilibrium. Comparison with equations developed for biogenic calcite give a similarly good fit. Linear regression with Craig's (1965) equation yields: t = ?0.07 + 1.01t? (r= 0.95) where t is the actual growth temperature and t? Is the calculated paleotemperature. The intercept and the slope of this linear equation show that the familiar paleotemperature equation developed originally for mollusca carbonate, is equally applicable for the planktonic foraminifer G. sacculifer.Second order regression of the culture temperature and the delta difference (δ18Oc ? δ18Ow) yield a correlation coefficient of r = 0.95: t? = 17.0 ? 4.52(δ18Oc ? δ18Ow) + 0.03(δ18Oc ? δ18Ow)2t?, δ18Oc and δ18Ow are the estimated temperature, the isotopic composition of the shell carbonate and the sea water respectively.A possible cause for nonequilibnum isotopic compositions reported earlier for living planktonic foraminifera is the improper combustion of the organic matter.  相似文献   

11.
The geochemical history of Lake Lisan, the Pleistocene precursor of the Dead Sea, has been studied by geological, chemical and isotopic methods.Aragonite laminae from the Lisan Formation yielded (equivalent) Sr/Ca ratios in the range 0.5 × 10?2?1 × 10?2, Na/Ca ratios from 3.6 × 10?3 to 9.2 × 10?3, δ18OPDB values between 1.5 and 7%. and δ13CPDB from ?7.7 to 3.4%..The distribution coefficient of Na+ between aragonite and aqueous solutions, λANa, is experimentally shown to be very sensitive to salinity and nearly temperature independent. Thus, Na/Ca in aragonite serves as a paleosalinity indicator.Sr/Ca ratios and δ18O values in aragonite provide good long-term monitors of a lake's evolution. They show Lake Lisan to be well mixed, highly evaporated and saline. Except for a diluted surface layer, the salinity of the lake was half that of the present Dead Sea (15 vs 31%).Lake Lisan evolved from a small, yet deep, hypersaline Dead Sea-like, water body. This initial lake was rapidly filled-up to its highest stand by fresh waters and existed for about 40,000 yr before shrinking back to the present Dead Sea. The chemistry of Lake Lisan at its stable stand represented a material balance between a Jordan-like input, an original large mass of salts and a chemical removal of aragonite. The weighted average depth of Lake Lisan is calculated, on a geochemical basis, to have been at least 400, preferably 600 m.The oxygen isotopic composition of Lake Lisan water, which was higher by at least 3%. than that of the Dead Sea, was probably dictated by a higher rate of evaporation.Na/Ca ratios in aragonite, which correlate well with δ13C values, but change frequently in time, reflect the existence of a short lived upper water layer of varying salinity in Lake Lisan.  相似文献   

12.
Natural malachite is a well defined solid demonstrating reproducible solubility behavior over a wide range of pH. The following equilibrium constants associated with the malachite dissolution equilibrium at 25°C, 1 atm were determined:
Ksp = a2cu2+aCO32?K2wa2H+ = 3.5 ± 0.6 × 10?34
(infinite dilution)
K1sp = [Cu2+]2[CO2?3]K2wa2H+ = 10. ± 0.2 × 10?32
(0.72 ionic strength)
K′sp = m2Cu2+mCOsu2?3K2wa2H+ = 1.3 ± 0.1 × 10?28
(36.9‰ salinity seawater). The temperature dependence of a “mixed” equilibrium constant, Ksp+, of the form:
K2sp = [Cu2+]2mCO2?3K2wa2H+
has been measured at I = 0.72, yielding the relationship:
log K2sp = (? 9.8 ± 0.03) × 104(1T°K) + (1.52 ± 0.09)
within a 5–25°C temperature range. The effect of pressure on the solubility of malachite in water and seawater was estimated from partial molar volume and compressibility data. For 25 °C at infinite dilution K'sp (1000 bar)K'sp(0) = 240 and in seawater K′sp(1000)K'sp(0) = 44.Comparison of stoichiometric and apparent malachite equilibrium constants has been used to estimate the extent of copper(II) ion interaction at the ionic strength of seawater. In dilute carbonate medium (total alkalinity, TA = 2.4 meq/kg H2O, pH 8.3), 2.9% of total dissolved copper exists as the free copper(II) ion and in seawater (S = 36.9%., TA = 2.3 meq/kg H2O, pH = 8.1), [Cu2+]T(Cu) is 3.1%.Total dissolved copper levels of approximately 450–750 nMol/Kg are necessary to attain malachite saturation conditions in the open ocean. Observations of malachite particles suspended in seawater must be explained by precipitation or solid phase substitution reactions from localized environments rather than by direct precipitation from bulk seawater.  相似文献   

13.
Hydrogen which is highly enriched in deuterium is present in organic matter in a variety of meteorites including non-carbonaceous chondrites. The concentrations of this hydrogen are quite large. For example Renazzo contains 140 μmoles/g of the 10,000‰ δD hydrogen. The DH ratios of hydrogen in the organic matter vary from 8 × 10?5 to 170 × 10?5 (δD ranges from ? 500‰ to 10,000‰) as compared to 16 × 10?5 for terrestrial hydrogen and 2 × 10?5 for cosmic hydrogen. The majority of the unequilibrated primitive meteorites contain hydrogen whose DH ratios are greater than 30 × 10?5. If the DH ratios in these compounds were due to enrichment relative to cosmic hydrogen by isotope exchange reactions, it would require that these reactions take place below 150 K. In addition the organic compounds having DH ratios above 50 × 10?5 would require temperatures of formation of < 120 K. These types of deuterium enrichments must take place by ion-molecule reactions in interstellar clouds where both ionization and low temperatures exist. Astronomically observed DH ratios in organic compounds in interstellar clouds are typically 180 × 10?5 and range between about 40 × 10?5 and 5000 × 10?5. The DH values we have determined are the lower limits for the organic compounds derived from interstellar molecules because all processes subsequent to their formation, including terrestrial contamination, decrease their DH ratios.In contrast, the DH ratios of hydrogen associated with hydrated silicates are relatively uniform for the meteorites we have analyzed with an average value of 14 × 10?5; very similar to the terrestrial value. These phyllosilicates values suggest equilibration of H2O with H2 in the solar nebula at temperatures of about 200 K and higher.The 13C12C ratios of organic matter, irrespective its DH ratio, lie well within those observed for the earth. If organic matter originated in the interstellar medium, our data would indicate that the 13C12C ratio of interstellar carbon five billion years ago was similar to the present terrestrial value.Our findings suggest that other interstellar material, representing various inputs from various stars, in addition to the organic matter is preserved and is present in the meteorites which contain the high DH ratios. We feel that some elements existing in trace quantities which possess isotopic anomalies in the meteorites may very well be such materials.  相似文献   

14.
Equations are developed for calculating the density of aluminosilicate liquids as a function of composition and temperature. The mean molar volume at reference temperature Tr, is given by Vr = ∑XiV?oi + XAV?oA, where the summation is taken over all oxide components except A12O3, X stands for mole fraction, V?oi terms are constants derived independently from an analysis of volume-composition relations in alumina-free silicate liquids, and V?oA is the composition-dependent apparent partial molar volume of Al2O3. The thermal expansion coefficient of aluminosilicate liquids is given by α = ∑Xi\?gaio + XA\?gaAo, where \?gaio terms are constants independent of temperature and composition, and \?gaoA is a composition-dependent term representing the effect of Al2O3 on the thermal expansion. Parameters necessary to calculate the volume of silicate liquids at any temperature T according to V(T) = Vrexp[α(T-Tr)], where Tr = 1400°C have been evaluated by least-square analysis of selected density measurements in aluminosilicate melts. Mean molar volumes of aluminosilicate liquids calculated according to the model equation conform to experimentally measured volumes with a root mean square difference of 0.28 ccmole and an average absolute difference of 0.90% for 248 experimental observations. The compositional dependence of V?oA is discussed in terms of several possible interpretations of the structural role of Al3+ in aluminosilicate melts.  相似文献   

15.
The spectrophotometric measurements of chloro complexes of lead in aqueous HCl, NaCl, MgCl2 and CaCl2 solutions at 25°C have been analyzed using Pitzer's specific interaction equations. Parameters for activity coefficients of the complexes PbCl+, PbCl20 and PbCl3? have been determined for the various media. Values of K1 = 30.0 ± 0.6, K2 = 106.7 ± 2.1 and K3 = 73.0 ± 1.5 were obtained for the cumulative formation constants. [Pb2+ + nCl? → PbCln2?n)]. These values are in reasonable agreement with literature data. The Pitzer parameters for the PbCl ion pairs in various media were used to calculate the speciation of Pb2+ in an artificial seawater solution.  相似文献   

16.
The effect of presure on the solubility of minerals in water and seawater can be estimated from In
(KPspK0sp) + (?ΔVP + 0.5ΔKP2)RT
where the volume (ΔV) and compressibility (ΔK) changes at atmospheric pressure (P = 0) are given by
ΔV = V?(M+, X?) ? V?[MX(s)]ΔK = K?(M+, X?) ? K?[MX(s)]
Values of the partial molal volume (V?) and compressibilty (K?) in water and seawater have been tabulated for some ions from 0 to 50°C. The compressibility change is quite large (~10 × 10?3 cm3 bar?1 mol?1) for the solubility of most minerals. This large compressibility change accounts for the large differences observed between values of ΔV obtained from linear plots of In Ksp versus P and molal volume data (Macdonald and North, 1974; North, 1974). Calculated values of KPspKosp for the solubility of CaCO3, SrSO4 and CaF2 in water were found to be in good agreement with direct measurements (Macdonald and North, 1974). Similar calculations for the solubility of minerals in seawater are also in good agreement with direct measurements (Ingle, 1975) providing that the surface of the solid phase is not appreciably altered.  相似文献   

17.
The performance characteristics of PANURGE, a modified CAMECA IMS3F ion microprobe, have been studied at a mass resolving power of 5000 for the purpose of determining isotopic ratios at a precision level approaching that of counting statistics using beam switching. The techniques used for this type of measurement are described. Using this approach, the isotopic composition of Mg and Si and the atomic ratio of AlMg in minerals from the Allende inclusion WA and the Allende FUN inclusion Cl have been measured with the ion microprobe at high mass resolving power. Enrichments in 26Mg of up to 260%. have been found. Mg and AlMg measurements on cogenetic spinel inclusions and host plagioclase crystals yield Mg-Al isochrons in excellent agreement with precise mineral isochrons determined by thermal emission mass spectrometry. The measurements confirm the presence of substantial excess 26Mg in WA (26Mg127Al = 5 × 10?5) and its near absence in Cl (26Mg127Al < 4 × 10?6). In WA plagioclase, data for which 27Al24Mg = 300 to 1000 define a linear array with 26Mg127Al = 3 × 105 and with initial 26Mg24Mg composition 30%. greater than in high Mg phases. This suggests a metamorphic reequilibration of Mg in Allende plagioclase at least 0.6 my after WA formation. There were no variations in detected 26Mg127Al in WA plagioclase associated with concentration of 26Mg1 into isolated clusters. We have confirmed by ion probe measurements that the Mg composition in Allende Cl is highly fractionated and is uniform among pyroxene, melilite, plagioclase, spinel crystals and spinel included in melilite and plagioclase crystals. Likewise, the Si composition is mass fractionated and is the same in pyroxene, melilite and plagioclase.  相似文献   

18.
Determination of amorphous silica solubility in acidified ferric nitrate solutions confirms the presence of ferric silicate complexing. A dissociation constant for the reaction:
FeH3SiO42+Fe3+ + H3SiO4?
of 10?9.8 ± 0.3 pK units at room temperature (22 ± 3°C) is obtained, in close agreement with reported values at 25°C corrected to zero ionic strength of 10?9.9 by Weber and Stumm and 10?9.5 by Olson and O'Melia. Iron-silicate complexing may be of significance to the mobilization of silica in acid waters associated with oxidizing sulphide deposits and coal strip mining and the precipitation of secondary silicate mineral phases.  相似文献   

19.
The isotopic composition of Ag and the concentration of Ag and Pd have been determined in Canyon Diablo (IA), Grant (IIIB), Hoba, Santa Clara, Tlacotepec and Warburton Range (IVB), Piñon and Deep Springs (anom.). Troilite from Grant and Santa Clara have also been analyzed. All of these meteorites, with the exception of Canyon Diablo, give 107Ag109Ag in the metal phase that is greater than the terrestrial value with the enrichments of 107Ag ranging from ~2% to 212%. These data show that Ag of anomalous isotopic composition is common to all IVB and anomalous meteorites. The results on Grant suggest that the anomalies may be widespread including more common meteorite groups. There is a general correlation of 107Ag109Ag with PdAg except for the data from FeS of Santa Clara. It is concluded that the excess 107Ag is the result of decay of 107Pd, a nuclide that is extinct at present with an abundance of 107Pd108Pd of about 3 × 10?5. The troilite in Grant exhibits normal 107Ag109Ag to within errors, a high Ag concentration and a low ratio of 108Pd109Ag ~0.17. Grant metal has 107Ag109Ag that is ~2% greater than normal and a high ratio of 108Pd109Ag ~ 103. The data from Grant appear to represent a 107Pd-107Ag isochron and indicate that the cooling rate at elevated temperatures was sufficiently rapid to preserve substantial isotopic differences between metal and troilite. Troilite in Santa Clara was found to contain Ag with a very high 107Ag109Ag ratio (108% above normal), an Ag concentration only a factor of three above the metal and a high value of 108Pd109Ag ~1.3 × 104. The troilite has a higher 107Ag109Ag than the metal. These data are not compatible with a simple model of in situ decay and subsequent local Ag redistribution between metal and troilite during cooling. These data suggest that Ag in Santa Clara and possibly other IVB meteorites is made up of almost pure 107Ag produced from 107Pd decay and 109Ag produced by nuclear reactions with only a small amount of “normal” Ag. This indicates an intense energetic particle bombardment history in the early solar system (~1020 p/m2) which occurred after the formation of small planetary bodies. We infer that a T-Tauri activity by the early sun contributed to some late stage “nucleosynthesis” and the heating of a dust cloud. In addition, implications on the early thermal evolution of iron meteorites are presented based on 107Pd decay and models of the cooling history.  相似文献   

20.
Noble gas data are reported for 12 E-chondrites. Combined with literature data, they show that K-Ar ages are >4 Æ for 14 out of 18 meteorites, yet U, Th-He ages are often shorter, perhaps due to late, mild reheating. Cosmic-ray exposure ages differ systematically between types 4 and 6, with E4's mostly below 16 Myr and E6's above 30 Myr. This may mean that the E-chondrite parent body contains predominantly a single petrologic type on the (~ 1 km) scale of individual impacts, in contrast to the more thoroughly mixed parent bodies of the ordinary chondrites.The heavy noble gases consist of at least two primordial components: the usual planetary component (36Ar132Xe ~ 80) and a less fractionated, ‘subsolar’ component (2700 ≤ 36Ar132Xe ≤ 3800). The latter is found in highest concentration in the E4 chondrite South Oman (36Ar = 760 × 10?8cc/g, 36Ar132Xe = 2700). The isotopic compositions of both components are similar to typical planetary values, indicating that some factor other than mass controlled the noble gas elemental ratios. The heavy Xe isotopes occasionally show some of the lowest 134Xe132Xe and 136Xe132Xe ratios measured in bulk chondrites, suggestive of nearly fission-free Xe (e.g. 136Xe132Xe = 0.3095 ± 0.0020). Amounts of planetary gas in E4 E6 chondrites fall in the range for ordinary chondrites of types 4–6, but, in contrast to the ordinary chondrites. fail to correlate with petrologic type or volatile trace element contents. Another unusual feature of E-chondrites is that primordial Ne is present even in most 4's and 5's (20Nep ~ 1 to 7 × 10?8cc/g). with an isotopic composition consistent with planetary Ne.Analyses of mineral separates show that the planetary gases are concentrated in an HF- and HCl-insoluble mineral similar to phase Q, the poorly characterized, HNO3-soluble carrier of primordial gases in carbonaceous and ordinary chondrites. The subsolar gases, on the other hand, are located in an HCl- and HNO3-resistant phase, possibly enstatite or a minor phase included in enstatite. Much of the 129Xer (50% for E4's, > 70% for E6's) is in HCl-resistant but HF-soluble sites, suggestive of a silicate.A similar subsolar component may be responsible for the high 36Ar132Xe ratios of some C3's, unequilibrated ordinary chondrites, and the unique aubrite Shallowater. The planet Venus also has a high ArKr ratio, well above the planetary range, and hence may have acquired its noble gases from an E-chondrite-like material, similar to South Oman.  相似文献   

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