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1.
《Applied Geochemistry》1998,13(2):155-164
Two issues are addressed in this paper: the solid/liquid distribution behaviour of radiocaesium (137Cs and 134Cs) and radiostrontium (90Sr) in sapropels, and the potential effectiveness of sapropels as amendments to remediate soils contaminated with these radionuclides. It is shown that the solid/liquid partitioning of radiocaesium and radiostrontium in sapropels is governed by the same processes as in soils. Experimental KD values measured in a representative solution vary between 300 and 5000 dm3 kg−1 for radiocaesium and between 15 and 50 dm kg−1 for radiostrontium. These KD values can be interpreted quantitatively on the basis of the main factors which govern the solid/liquid partitioning of these radionuclides.This quantitative approach also allows predictions to be made on the potential effectiveness of sapropel amendments in contaminated soils. These predictions agree very well with experimental results from simple laboratory experiments aimed at investigating the amendment effect. Addition of 1–4 wt.% doses of 2 sapropel samples with different radiocaesium retention characteristics had no significant effect on the radiocaesium distribution coefficient in sandy soils. It is therefore expected that the addition of such sapropels will not result in a decrease of the radiocaesium soil-to-plant transfer, at least not from the point of view of the increase of the radiocaesium retention in the amended soil. Addition of 1–4 wt.% doses of a high CEC sapropel to low CEC sandy soils increased the radiostrontium distribution coefficient up to 3.5 times. It can thus be expected that addition of such high CEC sapropel will increase the radiostrontium retention in the amended soil, and thus decrease the radiostrontium soil-to-plant transfer.  相似文献   

2.
《Applied Geochemistry》1996,11(4):589-594
A comparative study is presented on the quantitative characterisation procedures of soils and sediments in terms of specific radiocaesium sorption potentials obtained during elaborate procedures, which include masking techniques, and a simplified protocol relying on a single KD137Csmeasurement. The elaborate and simple procedures were compared for some 120 soils and sediments of widely different origin, covering some three orders of magnitude in specific sorption capacities. The excellent agreement between both procedures provides the basis for a new and simple characterisation procedure which can be used in routine application.  相似文献   

3.
The desorption of 137Cs+ was investigated on sediments from the United States Hanford site. Pristine sediments and ones that were contaminated by the accidental release of alkaline 137Cs+-containing high level nuclear wastes (HLW, 2 × 106 to 6 × 107 pCi 137Cs+/g) were studied. The desorption of 137Cs+ was measured in Na+, K+, Rb+, and NH4+electrolytes of variable concentration and pH, and in presence of a strong Cs+-specific sorbent (self-assembled monolayer on a mesoporous support, SAMMS). 137Cs+ desorption from the HLW-contaminated Hanford sediments exhibited two distinct phases: an initial instantaneous release followed by a slow kinetic process. The extent of 137Cs+ desorption increased with increasing electrolyte concentration and followed a trend of Rb+ ≥ K+ > Na+ at circumneutral pH. This trend followed the respective selectivities of these cations for the sediment. The extent and rate of 137Cs+ desorption was influenced by surface armoring, intraparticle diffusion, and the collapse of edge-interlayer sites in solutions containing K+, Rb+, or NH4+. Scanning electron microscopic analysis revealed HLW-induced precipitation of secondary aluminosilicates on the edges and basal planes of micaceous minerals that were primary Cs+ sorbents. The removal of these precipitates by acidified ammonium oxalate extraction significantly increased the long-term desorption rate and extent. X-ray microprobe analyses of Cs+-sorbed micas showed that the 137Cs+ distributed not only on mica edges, but also within internal channels parallel to the basal plane, implying intraparticle diffusive migration of 137Cs+. Controlled desorption experiments using Cs+-spiked pristine sediment indicated that the 137Cs+ diffusion rate was fast in Na+-electrolyte, but much slower in the presence of K+ or Rb+, suggesting an effect of edge-interlayer collapse. An intraparticle diffusion model coupled with a two-site cation exchange model was used to interpret the experimental results. Model simulations suggested that about 40% of total sorbed 137Cs+ was exchangeable, including equilibrium and kinetic desorbable pools. At pH 3, this ratio increased to 60-80%. The remainder of the sorbed 137Cs+ was fixed or desorbed at much slower rate than our experiments could detect.  相似文献   

4.
The apparent equilibrium constant for the exchange of Fe and Ni between coexisting olivine and sulfide liquid (KD = (XNiS/XFeS)liquid/(XNiSi12O2/XFeSi12O2)olivine; Xi = mole fraction) has been measured at controlled oxygen and sulfur fugacities (fO2 = 10−8.1 to 10−10 and fS2 = 10−0.9 to 10−1.7) over the temperature range 1200 to 1385°C, with 5 to 37 wt% Ni and 7 to 18 wt% Cu in the sulfide liquid. At log fO2 of −8.7 ± 0.1, and log fS2 of −0.9 to −1.7, KD is relatively insensitive to sulfur fugacity, but comparison with previous results shows that KD increases at very low sulfur fugacities. KD values show an increase with the nickel content of the sulfide liquid, but this effect is more complex than found previously, and is greatest at log fO2 of −8.1, lessens with decreasing fO2, and KD becomes independent of melt Ni content at log fO2 ≤ −9.5. The origin of this variation in KD with fO2 and fS2 is most likely the result of nonideal mixing of Fe and Ni species in the sulfide liquid. Such behavior causes activity coefficients to change with either melt oxygen content or metal/sulfur ratio, effects that are well documented for metal-rich sulfide melts.Application of these experimental results to natural samples shows that the relatively large dispersion that exists in KD values from different olivine + sulfide-saturated rock suites can be interpreted as arising from variations in fO2, fS2, and the nickel content of the sulfide liquid. Estimates of fO2 based on KD and sulfide melt composition in natural samples yields a range from fayalite-magnetite-quartz (FMQ)-1 to FMQ-2 or lower, which is in good agreement with previous values determined for oceanic basalts that use glass ferric/ferrous ratios. Anomalously high KD values recorded in some suites, such as Disko Island, probably reflect low fS2 during sulfide saturation, which is consistent with indications of low fO2 for those samples. It is concluded that the variation in KD values from natural samples reflects olivine-sulfide melt equilibrium at conditions within the T-fO2-fS2 range of terrestrial mafic magmas.  相似文献   

5.
The Nernst partition coefficient of nickel (DNi) between Cr-spinel and silicate melt in natural systems has been investigated using mid-ocean ridge basalts (MORB) and other volcanic rocks. The Cr-spinel/olivine DNi values in volcanic rocks are between 1.2 and 0.3, indicating that the Cr-spinel/liquid DNi values vary from slightly higher to significantly lower than the olivine/liquid DNi values in natural systems. The Cr-spinel/liquid DNi values from the MORB samples vary between 6 and 11, slightly higher than those from the S-bearing experiments of Satari et al. [Satari P., Brenan J. M., Horn I. and McDonough W. F. (2002) Experimental constraints on the sulfide- and chromite-silicate melt partitioning behavior of rhenium and platinum-group elements. Economic Geology97, 385-398]. The results of the MORB samples and the experiments of Satari et al. (2002) indicate a negative correlation between the Cr-spinel/liquid DNi and the XCr values in Cr-spinels (Cr cation number on the basis of 3 total cations in the spinel structure). Variations of Cr-spinel/liquid DNi values with Cr-spinel compositions can be estimated from an empirical equation based on the results of the MORB samples and the experiments by Satari et al. (2002). The choice of Cr-spinel/liquid DNi = 10 for numerical modeling by Righter et al. [Righter K., Leeman W. P. and Hervig R. L. (2006) Partitioning of Ni, Co, and V between spinel-structured oxides and silicate melts: importance of spinel composition. Chemical Geology227, 1-25] is reasonable for basaltic systems. For picritic and komatiitic systems a lower value of ∼5 is more appropriate.  相似文献   

6.
The measurement of diffusion coefficients for Na, K, Rb and Cs has been realized by the technique of active salt deposits on glasses of albite and orthoclase composition, at normal pressure and in the temperature range 300–1000°C. The values of D are between 10?6 and 10?12 cm2 s?1 and, for every type of run, they vary with temperature according to Arrhenius laws, with activation energies ranging from 13 to 68 kcal mole?1. These important variations are related to the size of the diffusing element (at 700°C in albite glass DNa/DK/DRbDCs ～- 107/105/103/1) and to the size of the major alkali element (for rubidium at 800°C Dor·gl/Dab·gl ～- 20). By comparison with available data on diffusion in feldspars, we emphasize the influence of the defect density on the diffusion process.  相似文献   

7.
The iron-magnesium distribution coefficient, $$K'_D = (X_{\Sigma {\text{FeO}}} /X_{{\text{MgO}}} )^{{\text{olivine}}} (X_{{\text{MgO}}} /X_{\Sigma {\text{FeO}}} )^{{\text{liquid}}} ,$$ has frequently been used as a means of testing whether experimental and natural silicate liquids could have been in equilibrium with olivine of mantle composition. It is shown here that this K′ D decreases with increasing oxygen fugacity (xxx) for a hydrous partial melt in equilibrium with a natural spinel peridotite assemblage under pressure and temperature conditions corresponding to those of the upper mantle (from 0.52 at the xxx of the iron-wüstite buffer to 0.04 at the xxx of the magnetite-hematite buffer). K′ D also increases with increasing pressure, with decreasing temperature, and probably with increasing Mg/(Mg+∑ Fe) of the parental peridotite, suggesting that $$K_D = (X_{{\text{FeO}}} /X_{{\text{MgO}}} )^{{\text{olivine}}} (X_{{\text{MgO}}} /X_{{\text{FeO}}} )^{{\text{liquid}}}$$ also increases with increasing pressure and decreasing temperature. Thus, unless these four variables (P, T, xxx, silicate composition) are known for a natural magma, K′ D and probably K D are variables, and the Mg/(Mg+∑ Fe) of such a magma cannot be correlated to that of the parent. The K D determined at 1 atm pressure by Roeder and Emslie has frequently been used to test whether the Mg/(Mg+∑ Fe) ratios of experimentally formed liquids at high pressure in equilibrium with olivine of known Fo content represent the equilibrium Mg/(Mg+Fe2+) of this liquid, assuming that ∑Fe=Fe2+ and that K′ D does not vary with P, T, and composition of the system. Published data demonstrate that the oxygen fugacities of the experimental designs employed by different laboratories vary between those of the magnetite-hematite and magnetite-wüstite buffers (6 orders of magnitude), resulting in K′ D between 0.04 and 0.31 at 1050° C and 15 kbar, for example. Thus, published arguments as to whether the quenched liquids represent equilibrium compositions based on iron-magnesium partitioning are inadequate. The effects of P, T, xxx, and the composition of the starting material must also be considered.  相似文献   

8.
Partitioning of manganese between forsterite and silicate liquid   总被引：1，自引：0，他引：1  
Partition coefficients for Mn between forsterite and liquid in the system MgO-CaO-Na2O-Al2O3-SiO2 (+ about 0.2% Mn) were measured by electron microprobe for a variety of melt compositions over the temperature range 1250–1450°C at one atm pressure. The forsterite-liquid partition coefficient of Mn (mole ratio, MnO in Fo/MnO in liquid, designated Dmnfo?Liq) depends on liquid composition as well as temperature: at 1350°C, DMnFo?Liqranges from 0.60 (basic melt, SiO2 = 47wt%) to 1.24 (acidic melt, SiO2 = 65wt%). At lower temperatures, the partition coefficient is more strongly dependent on melt composition.The effects of melt composition and temperature on DMnfo?Liq can be separately evaluated by use of the Si:O atomic ratio of the melts. A plot of DmnFo?Liq measured at various temperatures vs melt Si:O for numerous liquid compositions reveals discrete, constant-temperature curves that are not well defined by plotting DMnFo?Liq against other melt composition parameters such as melt basicity or MgO content. For constant Si:O in the melt, In DMnFo?Liq vs reciprocal absolute temperature is linear; however, the slope of the plot becomes more positive for higher values of Si:O, indicating a higher energy state for Mn2+ ions in acidic melts than in basic melts.Comparison of Mn partitioning data for the iron-free system used in this study with data of other workers on iron-bearing compositions suggests that the effect of iron on Mn partitioning between olivine and melt is small over the range of basalt liquidus temperatures.  相似文献   

9.
Soil n-alkane δD vs. altitude gradients along Mount Gongga, China   总被引：1，自引：0，他引：1  
The altitude effect on the isotopic composition of precipitation and its application to paleoelevation reconstruction using authigenic or pedogenic minerals have been intensively studied. However, there are still no studies on variations in biomarker δD along altitude transects to investigate its potential as a paleoelevation indicator, although it has been observed that δD of higher plant lipid may record changes in precipitation δD (δDp). Here, we present δD values of higher plant-derived C27, C29, and C31n-alkanes from surface soil along the eastern slope of Mount Gongga, China with great changes in physical variables and vegetation over a range from 1000 to 4000 m above sea level. The weighted-mean δD values of these n-alkanes (δDwax) show significant linear correlations with predicted δDp values (R2 = 0.76) with an apparent isotopic enrichment (εwax-p) of −137 ± 9‰, indicating that soil δDwax values track overall δDp variation along the entire altitudinal transect. Leaf δDwax is also highly correlated with mountain altitude by a significant quadratic relationship (R2 = 0.80). Evapotranspiration is found declining with altitude, potentially lowering δDwax values at higher elevations. However, this evapotranspiration effect is believed to be largely compensated by the opposing effect of vegetation changes, resulting in less varied εwax-p values over the slope transect. This study therefore confirms the potential of using leaf δDwax to infer paleoelevations, and more generally, to infer the δD of precipitation.  相似文献   

10.
Adsorption of trace amounts of radiocaesium on NH4-, K-, and Na-saturated Fithian illite and subsequent desorption by 1 M NH4 showed that a substantial amount of radiocaesium (44%, 46%, and 91% for NH4-, K-, and Na-illite, respectively) cannot be desorbed after only 5 min of adsorption. Our results suggest that this instantaneous fixation is caused by the collapse of the frayed edges of the clay mineral and the relatively high concentration of radiocaesium building up in solution in the batch desorption experiments. Consequently, commonly applied high-NH4 extractions underestimate truly exchangeable amounts of radiocaesium in soils and sediments containing illitic clay minerals. The rate of desorption of trace amounts of radiocaesium from the solids using high NH4 or Cs concentrations has a half-life of about 2 yr, reflecting radiocaesium desorption from (partially) collapsed interlayers. Extraction of radiocaesium from illite after 5 min of contact time with a Cs-selective adsorbent or a 1 × 10-6 M CsCl solution shows that 100% of the bound radiocaesium is readily available. The desorption rate in the presence of a Cs-selective adsorbent has a half-life of about 0.2 yr. Desorption of radiocaesium from illite using different ammonium concentrations shows that radiocaesium partitioning follows reversible ion-exchange theory if the NH4 concentration is below 1 × 10-4 M, and sufficient time (weeks) is allowed for the reaction to proceed. Thus, radiocaesium sorption reversibility in the natural environment is much higher than generally assumed, and equilibrium solid/liquid partitioning may be assumed for the long-term modelling of radiocaesium mobility in the natural environment. In the particular case of anoxic freshwater sediments with very high NH4 concentrations in the pore waters (up to several mmol.L-1), collapse of the frayed edges of illite may occur, influencing radiocaesium partitioning. If collapse occurs before radiocaesium adsorbs to illite, high caesium sorption reversibility as measured by high-NH4 extraction can be expected because further collapse of the frayed edges during the extraction procedure will be limited. This effect has indeed been observed earlier in the extraction of radiocaesium from anoxic freshwater sediments with high-NH4 solutions and was as yet unexplained.  相似文献   

11.
Published data on the distribution of Fe and Mg between the two distinct octahedral sites (M1 and M2) in orthopyroxenes show that the equilibrium Fe-Mg distribution coefficient (KD) is roughly constant at intermediate ferrosilite content (XFs of 0.2 to 0.6) but at low XFs (<0.2) is either anomalously high (Mössbauer data) or low (XRD data) compared to KD at intermediate XFs. We report an experimental study on the equilibrium KD values for two natural single crystals of orthopyroxene (with XFs of 0.011 and 0.160) using a high-sensitivity Mössbauer spectrometer. The KD values were determined at 1 bar and temperatures between 600 and 1000°C, and reversed at 600 to 900°C. The values are found to be independent of orthopyroxene composition at a given temperature within analytical uncertainties, and in agreement with KD values at intermediate XFs. A least-squares fit to the KD data yields: lnKD = 0.391(±0.131) − 2205(±141)/T, where T is temperature in K, and uncertainties are at the 2σ level. This equation is valid for XFs values up to at least 0.6. We suggest that previous Mössbauer and XRD data at low XFs were compromised by analytical difficulties. The new result that KD is roughly independent of XFs greatly simplifies treatment of equilibrium and speedometry based on Fe-Mg order-disorder in orthopyroxene.  相似文献   

12.
In the DI-A2 experiment several non-reactive and reactive tracers were injected as a pulse in a packed-off borehole in the Opalinus Clay. Unlike the previous DI-A1 test, the design of the Teflon filter in the injection borehole forced the water to flow through the filter and the open space between the filter and the borehole wall (the filter itself did not act as a diffusion barrier between the circulating solution and the rock). The decrease in tracer concentration in the liquid phase was monitored during a period of a year. Afterwards, the borehole section was overcored and the tracer profiles in the rock were analyzed. A main interest of this experiment was to understand the chemical behavior of sorbing tracers: Cs+ (stable), 85Sr2+, 60Co2+ and Eu3+ (stable). The complete dataset (except for Eu3+ because of strong sorption to experimental equipment) was analyzed in a previous study with a 2D diffusion–reaction model and the derived diffusion and sorption parameters were compared with laboratory data. As in DI-A1, a difference by a factor of about 2 for sorption (magnitude of the Freundlich isotherm) was obtained between in situ and laboratory batch sorption experiments.Recent experimental and modeling studies have shown equivalent Cs+ sorption on intact and disaggregated Opalinus Clay samples. In view of these developments, new modeling of Cs+ diffusion and retention in the DI-A2 experiment has been performed using CrunchFlow. The calculations include transport by diffusion and a multisite cation exchange model to account for the retention of Cs+. The new results show that upscaling of Cs+ sorption from laboratory to field is no longer required. However, a difference in sorption by a factor of about 2 is still explained by the use of different versions of the same cation exchange model (a small difference in the selectivity coefficient for one type of site). This uncertainty in sorption leads to an uncertainty in the effective diffusion coefficient (De) for Cs+, also by a factor of 2 (2–4 × 10−10 m2/s). Clearly, the values of De obtained are correlated with the strength of sorption in the model, with stronger sorption leading to larger De values. Discrimination between the two versions of the exchange model is not possible when using only the results of the in situ test. Additionally, during early times (t < 10 days) the drop in Cs+ concentration in the circulation system is slower than expected. Due to the experimental setup, this slow decrease in concentration cannot be caused by the filter in the contact between borehole and rock. Poor mixing in the circulation system could explain this effect.  相似文献   

13.
The effect of caustic NaNO3 solutions on the sorption of 137Cs to a Hanford site micaceous subsurface sediment was investigated as a function of base exposure time (up to 168 d), temperature (10°C or 50°C), and NaOH concentration (0.1 mol/L to 3 mol/L). At 10°C and 0.1 M NaOH, the slow evolution of [Al]aq was in stark contrast to the rapid increase and subsequent loss of [Al]aq observed at 50°C (regardless of base concentration). Exposure to 0.1 M NaOH at 10°C for up to 168 d exhibited little if any measurable effect on sediment mineralogy, Cs+ sorption, or Cs+ selectivity; sorption was well described with a two-site ion exchange model modified to include enthalpy effects. At 50°C, dissolution of phyllosilicate minerals increased with [OH]. A zeolite (tetranatrolite; Na2Al2Si3O10·2H2O) precipitated in 0.1 M NaOH after about 7 days, while an unnamed mineral phase (Na14Al12Si13O51·6H2O) precipitated after 4 and 2 days of exposure to 1 M and 3 M NaOH solutions, respectively. Short-term (16 h) Cs+ sorption isotherms (10−9-10−2 mol/L) were measured on sediment after exposure to 0.1 M NaOH for 56, 112, and 168 days at 50°C. There was a trend toward slightly lower conditional equilibrium exchange constants (Δlog NaCsKc ∼ 0.25) over the entire range of surface coverage, and a slight loss of high affinity sites (15%) after 168 days of pretreatment with 0.1 M base solution. Cs+ sorption to sediment over longer times was also measured at 50°C in the presence of NaOH (0.1 M, 1 M, and 3 M NaOH) at Cs+ concentrations selected to probe a range of adsorption densities. Model simulations of Cs+ sorption to the sediment in the presence of 0.1 M NaOH for 112 days slightly under-predicted sorption at the lower Cs+ adsorption densities. At the higher adsorption densities, model simulations under-predicted sorption by 57%. This under-prediction was surmised to be the result of tetranatrolite precipitation, and subsequent slow Na → Cs exchange. At higher OH concentrations, Cs+ sorption in the presence of base for 112 days was unexpectedly equal to, or greater than that expected for pristine sediment. The precipitation of secondary phases, coupled with the fairly unique mica distribution and quantity across all size-fractions in the Hanford sediment, appears to mitigate the impact of base dissolution on Cs+ sorption.  相似文献   

14.
几种镁铁矿物平衡共生的成分标志   总被引：3，自引：0，他引：3  
阎月华 《地质科学》1997,32(3):267-274
本文以晋冀内蒙边界地区变质岩中主要镁铁质造岩矿物辉石,闪石为例,阐明镁铁矿物平衡共生的一条普遍规律,即平衡共生的正辉石,钙闪石之间有相同的镁铁比,其分配系数等于或接近于1.引用冀东,吉南,泰山和南极凯西站等地的实例,论证了此规律同时存在于黑云母与钙闪石,黑云母与正辉石之间,也存在于辉长岩和花岗岩等岩浆岩的橄榄石和正辉石,角闪石与黑云母等矿物对之间。这是判断镁铁矿物是否平衡的成分标志。  相似文献   

15.
Crystalline primary inclusions in diamonds from the Argyle and Ellendale lamproites have been analyzed for Mn, Ni, Cu, Zn, Ga, Pb, Rb, Sr, Y, Zr, Nb, Ta, Ba and Mo by proton microprobe. Eclogite-suite inclusions dominate at Argyle and occur in equal proportions with peridotite-suite inclusions at Ellendale. Eclogitic phases present include garnet, omphacitic clinopyroxene, coesite, rutile, kyanite and sulfide. Eclogitic clinopyroxenes are commonly rich in K and contain 300–1060 ppm Sr and 3–70 ppm Zr: K/Rb increases with K content up to 1400 at 0.7–1.1% K. Rutiles have high Zr and Nb contents with Zr/Nb=1.5–4 and Nb/Ta 16. Of the peridotite-suite inclusions, olivine commonly contains > 10 ppm Sr and Mo; Cr-pyropes are depleted in Sr, Y and Zr, and enriched in Ni, relative to eclogitic garnets.Eclogite-suite diamonds grew in host rocks that were depleted in Mn, Ni and Cr, and enriched in Sr, Zn, Cu, Ga and Ti, relative to Type I eclogite xenoliths from the Roberts Victor Mine. Crystallization temperatures of the eclogite-suite diamonds, as determined by coexisting garnet and clinopyroxene from single diamonds, range from 1085 to 1575° C. Log K D (C i cpx /C i gnt ) varies linearly with 1/T for Zr, Sr and Ga in most of the same samples. This supports the validity of the temperature estimates; Argyle eclogite-suite diamonds have grown over a T range 400° C. Comparison with data from eclogite xenoliths in kimberlites suggests that K D Sr and K D Zr are mainly T-dependent, while K D Ga may be both temperature-and pressuredependent. K D Ni , K D Cu and K D Zn show no T dependence in these samples.In several cases, significant major-and/or trace-element disequilibrium is observed between different grains of the same mineral, or between pyroxene and garnet, within single diamonds. This implies that these diamonds grew in an open system; inclusions trapped at different stages of growth record changes in major and trace-element composition occurring in the host rock. Diamond growth may have been controlled by a fluid flux which introduced or liberated carbon and modified the composition of the rock. The wide range of equilibration temperatures and the range of composition recorded in the inclusions of single diamonds suggest that a significant time interval was involved in diamond growth.  相似文献   

16.
The divalent cation distribution in olivine (Mg, Fe)2SiO4 under high pressure and temperature was studied to clarify the detailed state of olivine in the mantle. Single crystal samples were heated for a sufficient period of time for the cations to migrate and quenched fast enough to preserve the equilibrated state under high pressures, and the crystal structure was determined with X-ray method. The pressure effect on the distribution coefficient K D[= (Fe/Mg) M1/(Fe/Mg) M2] was determined for the first time; dK D/dP?0.02 GPa?1. A set of five thermodynamic parameters required to describe the regular solution model was determined from data concerning the pressure dependence and the known temperature and compositional effects. As a result we have shown how K D depends on pressure, temperature, and composition. The notable feature clarified is the very large contribution of nonideality in the olivine solid solution. The K D of olivine crystals in the mantle is predicted; K D increases to ～ 2.2 at the depth of 400 km, in contrast to 0.9 ～ 1.2 of natural samples available at the surface of the Earth.  相似文献   

17.
Sorption of Cs to micaceous subsurface sediments from the Hanford site, USA   总被引：1，自引：0，他引：1  
The sorption of Cs+ was investigated over a large concentration range (10−9−10−2 mol/L) on subsurface sediments from a United States nuclear materials site (Hanford) where high-level nuclear wastes (HLW) have been accidentally released to the vadose zone. The sediment sorbs large amounts of radiocesium, but expedited migration has been observed when HLW (a NaNO3 brine) is the carrier. Cs+ sorption was measured on homoionic sediments (Na+, K+, Ca2+) with electrolyte concentrations ranging from 0.01 to 1.0 mol/L. In Na+ electrolyte, concentrations were extended to near saturation with NaNO3(s) (7.0 mol/L). The sediment contained nonexpansible (biotite, muscovite) and expansible (vermiculite, smectite) phyllosilicates. The sorption data were interpreted according to the frayed edge-planar site conceptual model. A four-parameter, two-site (high- and low-affinity) numeric ion exchange model was effective in describing the sorption data. The high-affinity sites were ascribed to wedge zones on the micas where particle edges have partially expanded due to the removal of interlayer cations during weathering, and the low-affinity ones to planar sites on the expansible clays. The electrolyte cations competed with Cs+ for both high- and low-affinity sites according to the trend K+ >> Na+ ≥ Ca2+. At high salt concentration, Cs+ adsorption occurred only on high-affinity sites. Na+ was an effective competitor for the high-affinity sites at high salt concentrations. In select experiments, silver-thiourea (AgTU) was used as a blocking agent to further isolate and characterize the high-affinity sites, but the method was found to be problematic. Mica particles were handpicked from the sediment, contacted with Cs+(aq), and analyzed by electron microprobe to identify phases and features important to Cs+ sorption. The microprobe study implied that biotite was the primary contributor of high-affinity sites because of its weathered periphery. The poly-phase sediment exhibited close similarity in ion selectivity to illite, which has been well studied, although its proportion of high-affinity sites relative to the cation exchange capacity (CEC) was lower than that of illite. Important insights are provided on how Na+ in HLW and indigenous K+ displaced from the sediments may act to expedite the migration of strongly sorbing Cs+ in subsurface environments.  相似文献   

18.
The relative incompatibility of Ar and K are fundamental parameters in understanding the degassing history of the mantle. Clinopyroxene is the main host for K in most of the upper mantle, playing an important role in controlling the K/Ar ratio of residual mantle and the subsequent time-integrated evolution of 40Ar/36Ar ratios. Clinopyroxene also contributes to the bulk Ar partition coefficient that controls the Ar degassing rate during mantle melting. The partitioning of Ar and K between clinopyroxene and quenched silicate melt has been experimentally determined from 1 to 8 GPa for the bulk compositions Ab80Di20 (80 mol% albite-20 mol% diopside) and Ab20Di80 with an ultraviolet laser ablation microprobe (UVLAMP) technique for Ar analysis and the ion microprobe for K. Data for Kr (UVLAMP) and Rb (ion probe) have also been determined to evaluate the role of crystal lattice sites in controlling partitioning. By excluding crystal analyses that show evidence of glass contamination, we find relatively constant Ar partition coefficients (DAr) of 2.6 × 10−4 to 3.9 × 10−4 for the Ab80Di20 system at pressures from 2 to 8 GPa. In the Ab20Di80 system, DAr shows similar low values of 7.0 × 10−5 and 3.0 × 10−4 at 1 to 3 GPa. All these values are several orders of magnitude lower than previous measurements on separated crystal-glass pairs.DK is 10 to 50 times greater than DRb for all experiments, and both elements follow parallel trends with increasing pressure, although these trends are significantly different in each system studied. The DK values for clinopyroxene are at least an order of magnitude greater than DAr under all conditions investigated here, but DAr appears to show more consistent behavior between the two systems than K or Rb. The partitioning behavior of K and Rb can be explained in terms of combined pressure, temperature, and crystal chemistry effects that result in changes for the size of the clinopyroxene M2 site. In the Ab20Di80 system, where clinopyroxene is diopside rich at all pressures, DK and DRb increase with pressure (and temperature) in an analogous fashion to the well-documented behavior of Na. For the Ab80Di20 system, the jadeite content of the clinopyroxene increases from 22 to 75 mol% with pressure resulting in a contraction of the M2 site. This has the effect of discriminating against the large K+ and Rb+ ions, thereby countering the effect of increasing pressure. As a consequence DK and DRb do not increase with pressure in this system.In contrast to the alkalis (Na, K, and Rb), DKr values are similar to DAr despite a large difference in atomic radius. This lack of discrimination (and the constant DAr over a range of crystal compositions) is also consistent with incorporation of these heavier noble gases at crystal lattice sites and a predicted consequence of their neutrality or “zero charge.” Combined with published DAr values for olivine, our results confirm that magma generation is an efficient mechanism for the removal of Ar from the uppermost 200 km of the mantle, and that K/Ar ratios in the residuum are controlled by the amount of clinopyroxene. Generally, Ar is more compatible than K during mantle melting because DAr for olivine is similar to DK for clinopyroxene. As a result, residual mantle that has experienced variable amounts of melt extraction may show considerable variability in time-integrated 36Ar/40Ar.  相似文献   

19.
Amphibole/liquid partition coefficients for the REE(Damph/liqREE) obtained from natural rocks increase systematically with bulk rock compositional change from basalt to rhyolite and are higher for the middle to heavy REE. Five new experimentally determined sets of DREE (La, Sm, “Eu2+”, Ho, Lu)and 4 published sets are similar to these data and provide values for use in geochemical modelling of magmatic processes involving amphibole, over a range of temperature, pressure and oxygen fugacity. The partition coefficients increase significantly with decreasing temperature, and increase slightly with increasing oxygen fugacity. Pressure does not appear to have a major effect, although one data set suggests increased pressure lowers Damph/liqREE in a basaltic composition.  相似文献   

20.
Summary Microprobe analyses and X-ray crystal structure refinement of terrestrial and lunar olivines are compared, in order to investigate the influence of temperature and composition on Mg-Fe2+ distribution between M1 and M2 sites.Quenching and heating experiments show that, for the same composition, a temperature increase causes an increase in the (Fe2+/Mg)M1/(Fe2+/Mg)M2 ratio (KD. Such experiments also demonstrate that the intracrystalline Mg-Fe2+ ordering in Ml and M2 sites is very fast and the calculated KD values therefore depend on cooling rate (C.R.), i.e., high KD values = high CR.. On the other hand, for the same cooling rate and temperature, Fe-rich olivine has a KD value higher than that of Mg-rich olivine, since Fe2+ is preferentially ordered in M1 site. Oxygen fugacity variations (QFI and QFM buffers) do not appreciably influence KD.The closure temperature of Mg-Fe2+ ordering between M1-M2 sites of olivine is probably lower than that estimated for orthopyroxene (c. 550–600°C; Saxena et al., 1989), owing to a lesser degree of non-equivalence between MI and M2 sites. The highest temperature that can be detected by KD values of natural olivines is 700–800 °C.
Einfluß von Temperatur und Zusammensetzung auf die Mg-Fe2+ Verteilung in Olivin
Zusammenfassung Mikrosondenuntersucbungen und Strukturverfeinerungen an terrestrischen und lunaren Olivinen werden verglichen, um den Einfluß von Temperatur und Zusammensetzung auf die Mg-Fe2+ Verteilung in der MI und M2 Position zu untersuchen. Experimentelle Untersuchungen belegen, daß bei gleichbleibender chemischer Zusamensetzung, eine Temperaturzunahme eine Zunahme im KD Verhältnis (Fe2+ /Mg)M1/(Fe2+/M9)M2 bedingt. Diese Experimente zeigen weiters, daß die Ordnung der Mg-Fe2+ Kationen im Gitter in den M 1 und M2 Positionen sehr rasch erfolgt und die berechnete KD Werte daher von der Abkühlungsrate (C.R.) abhängen; z. B. hohe KD-Werte = hohe C. R.Andererseits hat bei gleicher Abkühlungsrate und Temperatur Fe-reicher Olivin einen höheren KD Wert als Mg-reicher Olivin, da Fe2+ bevorzugt in die M1 Position eingebaut wird. änderungen in der Sauerstoff-Fugazität (QFI und QFM Buffer) beeinflussen die KD Werte unwesentlich.Die Schließungstemperaturen für die Mg-Fe2+ Ordnung zwischen der M1 und M2 Position in Olivin sind wahrscheinlich niedriger als die von Orthopyroxen (ca. 550–600°C;Saxena et al., 1989); dies wird mit einem niedrigeren Grad an non-equivalence von Ml und M2 erklärt. Die höchsten Temperaturen, die an Hand der KD-Werte an natürlichen Olivinen bestimmt wurden liegen bei 700–800°C.

With 2 Figures  相似文献   

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