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1.
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   

2.
The radioactive fission product, 137Cs, has been observed to mobilize from bottom sediments of two South Carolina reservoirs during summer thermal stratification and hypolimnetic anoxia. Mobilization is attributed to ion-exchange displacement of 137Cs from sediments by cations such as NH+4, Fe+2 and Mn+2 released under anaerobic conditions.Three types of 137Cs binding sites to sediment clay minerals are identified: 1) surface and planar sites from which 137Cs is generally exchangeable by all cations studied (Na+, NH+4, H+, Cs+, Ca+2, Mg+2, Fe+2, and Mn+2); 2) wedge sites where 137Cs exchange is sterically limited to cations of similar size and charge (NH+4, Cs+, K+, and perhaps H3O+); 3) interlayer sites from which 137Cs is not readily exchanged. More than 15 years after final 137Cs inputs, the reservoir sediments we studied showed the following percentage distribution of sites: 2 to 9% surface sites, 6 to 13% wedge sites, and 78 to 85% interlayer sites. In contrast, lake and stream sediments near Oak Ridge, Tennessee receiving 137Cs inputs more than 20 years earlier had greater than 99% of their 137Cs associated with non-exchangeable interlayer sites. The difference is attributed to the paucity in the South Carolina sediments of weathered micaceous clay minerals with their abundant interlayer sites. Such interlayer deficient clays are dominant in the Atlantic and Gulf coastal plains of the United States and elsewhere. This suggests that 137Cs will be physically and chemically more mobile in such areas as well as more biologically available. Mobility will be enhanced in regimes where cation inputs favoring 137Cs exchange occur. Subsurface waste disposal sites where anaerobic conditions develop with NH+4 production and Fe+2 and Mn+2 release might be such a regime.  相似文献   

3.
Cation partitioning and speciation in an aqueous soil suspension may depend on the coupling of reaction time, sorbate amount and mineral weathering reactions. These factors were varied in sediment suspension experiments to identify geochemical processes that affect migration of Sr2+ and Cs+ introduced to the subsurface by caustic high level radioactive waste (HLRW). Three glacio-fluvial and lacustrine sediments from the Hanford Site (WA, USA) were subjected to hyperalkaline (pH > 13), Na-Al-NO3-OH solution conditions within a gradient field of (i) sorptive concentration (10−5-10−3 m) and (ii) reaction time (0-365 d). Strontium uptake (qSr) exceeded that of cesium at nearly all reaction times. Sorbent affinity for both Cs+ and Sr2+ increased with clay plus silt content at early times, but a prolonged slow uptake process was observed over the course of sediment weathering that erased the texture effect for Sr2+; all sediments showed similar mass normalized uptake after several months of reaction time. Strontium became progressively recalcitrant to desorption after 92 d, with accumulation and aging of neoformed aluminosilicates. Formation of Cs+ and Sr2+-containing cancrinite and sodalite was observed after 183 d by SEM and synchrotron μ-XRF and μ-XRD. EXAFS data for qSr ≈ 40 mmol kg−1 showed incorporation of Sr2+ into both feldspathoid and SrCO3(s) coordination environments after one year. Adsorption was predominant at early times and low sorbate amount, whereas precipitation, controlled largely by sediment Si release, became increasingly important at longer times and higher sorbate amount. Kinetics of contaminant desorption at pH 8 from one year-weathered sediments showed significant dependence on background cation (Ca2+ versus K+) composition. Results of this study indicate that co-precipitation and ion exchange in neoformed aluminosilicates may be an important mechanism controlling Sr2+ and Cs+ mobility in siliceous sediments impacted by hyperalkaline HLRW.  相似文献   

4.
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   

5.
The distribution and dynamics of water molecules and monovalent cations (Li+, Na+, K+, Cs+, and H3O+) on muscovite surfaces were investigated by molecular dynamics (MD) simulations. The direct comparison of calculated X-ray reflectivity profiles and electron density profiles with experiments revealed the precise structure at the aqueous monovalent electrolyte solutions/muscovite interface. To explain the experimentally observed electron density profiles for the CsCl solution-muscovite interface, the co-adsorption of Cs+ and Cl− ion pairs would be necessary. Two types of inner-sphere complexes and one type of outer-sphere complex were observed for hydrated Li+ ions near the muscovite surface. For Na+, K+, Cs+, and H3O+ ions, the inner-sphere complexes were stable on the muscovite surface. The density oscillation of water molecules was observed to approximately 1.5 nm from the muscovite surface. The number of peaks and the locations for the density of water oxygen atoms were almost similar among the water molecules coordinated to Li+, Na+, K+, and H3O+ ions adsorbed on the muscovite surfaces. The water molecules around Cs+ ions that were adsorbed to muscovite surfaces seemed to avoid coordinating with Cs+ ions on the surface, and the density of water oxygen near the muscovite surface decreased relative to that in a bulk state. There was no significant difference in self-diffusion, viscosity, retention time, and reorientation time of water molecules among different cations adsorbed to muscovite surfaces. These translational and rotational motions of water molecules located at less than 1 nm from the muscovite surfaces were slower than those in a bulk state. A significant difference was observed for the exchange times of water molecules around monovalent cations. The exchange time of water molecules was long around Li+ ions and decreased with an increase in the ionic radius.  相似文献   

6.
Quantitative characterization of the development of proton surface charge on the surfaces of minerals is necessary for a fundamental understanding of reactions between minerals and aqueous electrolyte solutions. Despite many experimental studies of charge development, few attempts have been made to integrate the results of such studies with a theoretical framework that permits prediction. The present study builds on a theoretical framework to analyze a total of 55 sets of proton surface charge data referring to wide ranges of ionic strengths, and types of electrolyte and oxide. The resulting parameters were interpreted with the aid of crystal chemical, electrostatic, and thermodynamic theory, which enable a number of generalizations. Prediction of values of the pHZPC and ΔpKnθ reduces the number of triple-layer parameters to be estimated. New standard states for the equilibrium constants for electrolyte adsorption (KM+θ and KL−θ) permit direct comparison of samples with a range of surface areas or site densities. Predicted cation binding on high dielectric constant solids (e.g., rutile) shows KM+θ, increasing in the sequence Cs+, Rb+, K+, Na+, Li+. In contrast, on low dielectric constant solids (e.g., amorphous silica), the predicted sequence is Li+, Na+, K+, Rb+, Cs+. The opposite sequences are attributable to the large solvation energy contribution opposing adsorption on low-dielectric constant solids. Cation and anion binding constants are in general different, which enables direct prediction of the point-of-zero-salt effect (pHPZSE) relative to the pristine point-of-zero charge. The inner and outer capacitances in the triple-layer model (C1 and C2) are predictable parameters consistent with physically reasonable distances and interfacial dielectric constants for water. In summary, all the parameters in the triple-layer model can be estimated with the revised equations of this study, which enables prediction of proton surface charge for any oxide in 1:1 electrolyte solutions independent of experiments. Such predictions can serve as a complement to the experimental study of new oxide/electrolyte systems, or more complex systems, where additional mechanisms of charge development are likely.  相似文献   

7.
Nuclear waste that bore 90Sr2+ was accidentally leaked into the vadose zone at the Hanford site, and was immobilized at relatively shallow depths in sediments containing little apparent clay or silt-sized components. Sr2+, 90Sr2+, Mg2+, and Ca2+ was desorbed and total inorganic carbon concentration was monitored during the equilibration of this sediment with varying concentrations of Na+, Ca2+. A cation exchange model previously developed for similar sediments was applied to these results as a predictor of final solution compositions. The model included binary exchange reactions for the four operant cations and an equilibrium dissolution/precipitation reaction for calcite. The model successfully predicted the desorption data. The contaminated sediment was also examined using digital autoradiography, a sensitive tool for imaging the distribution of radioactivity. The exchanger phase containing 90Sr was found to consist of smectite formed from weathering of mesostasis glass in basaltic lithic fragments. These clasts are a significant component of Hanford formation sands. The relatively small but significant cation exchange capacity of these sediments was thus a consequence of reaction with physically sequestered clays in sediment that contained essentially no fine-grained material. The nature of this exchange component explained the relatively slow (scale of days) evolution of desorption solutions. The experimental and model results indicated that there is little risk of migration of 90Sr2+ to the water table.  相似文献   

8.
Powdered samples of some jarosite-type compounds were analysed at room temperature by 57Fe Mössbauer spectroscopy. This group of compounds is described by the formula: MFe3(SO4)2(OH)6, where M can be H3O+, Na+, K+, Rb+, Ag+, NH 4 + , Tl+, 1/2Pb2+ or 1/2Hg2+. Although all the spectra were very similar, a linear relationship between the quadrupole splitting and the iron content of the samples was observed for the monovalent jarosite-type compounds.  相似文献   

9.
《Applied Geochemistry》1996,11(4):601-603
An equation is presented for predicting solid/liquid distribution coefficients of radiocaesium on soils and sediments (freshwater and marine). The equation is based on the value of the radiocaesium interception potential of the illitic frayed edge sites of the system and liquid phase composition (K, NH4 and Na). The predictive potential of the equation is tested for some 130 combinations of soil/sediment and water composition covering a three-order-of-magnitude range in KD137Cs values. On average, experimental KD137Cs values exceed predicted values by a factor of 1.62 ± 0.75.  相似文献   

10.
Little work has been done on the influence of seiments on the basic chemical composition of overlying water mass.This paper deals with the vertical profile of the basic constituents such as Ca^ ,K^ ,Na^ ,and HCO3^-,as well as of pH in the overlying water mass and sediment porewater of Lake Lugu-a semi-closed,deep lake in Yunnan Province.The reand sediment porewater of Lake Lugu- a semi-closed,deep lake in Yunnan Province.The results revealed that those basic constituents may diffuse and transport from bottom sediments to overlying water mass through porewater.In the paper are also quantitatively evaluated the diffusive fluxes and the extent of their influence on overlying water mass,indicating that the lake sediment-water interface diffusion plays an important role in controlling the basic chemical composition of water in the whole lake.  相似文献   

11.
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12.
Radioactive core samples containing elevated concentrations of Cr from a high level nuclear waste plume in the Hanford vadose zone were studied to asses the future mobility of Cr. Cr(VI) is an important subsurface contaminant at the Hanford Site. The plume originated in 1969 by leakage of self-boiling supernate from a tank containing REDOX process waste. The supernate contained high concentrations of alkali (NaOH ≈ 5.25 mol/L), salt (NaNO3/NaNO2 >10 mol/L), aluminate [Al(OH)4− = 3.36 mol/L], Cr(VI) (0.413 mol/L), and 137Cs+ (6.51 × 10−5 mol/L). Water and acid extraction of the oxidized subsurface sediments indicated that a significant portion of the total Cr was associated with the solid phase. Mineralogic analyses, Cr valence speciation measurements by X-ray adsorption near edge structure (XANES) spectroscopy, and small column leaching studies were performed to identify the chemical retardation mechanism and leachability of Cr. While X-ray diffraction detected little mineralogic change to the sediments from waste reaction, scanning electron microscopy (SEM) showed that mineral particles within 5 m of the point of tank failure were coated with secondary, sodium aluminosilicate precipitates. The density of these precipitates decreased with distance from the source (e.g., beyond 10 m). The XANES and column studies demonstrated the reduction of 29-75% of the total Cr to insoluble Cr(III), and the apparent precipitation of up to 43% of the Cr(VI) as an unidentified, non-leachable phase. Both Cr(VI) reduction and Cr(VI) precipitation were greater in sediments closer to the leak source where significant mineral alteration was noted by SEM. These and other observations imply that basic mineral hydrolysis driven by large concentrations of OH− in the waste stream liberated Fe(II) from the otherwise oxidizing sediments that served as a reductant for CrO42−. The coarse-textured Hanford sediments contain silt-sized mineral phases (biotite, clinochlore, magnetite, and ilmenite) that are sources of Fe(II). Other dissolution products (e.g., Ba2+) or Al(OH)4− present in the waste stream may have induced Cr(VI) precipitation as pH moderated through mineral reaction. The results demonstrate that a minimum of 42% of the total Cr inventory in all of the samples was immobilized as Cr(III) and Cr(VI) precipitates that are unlikely to dissolve and migrate to groundwater under the low recharge conditions of the Hanford vadose zone.  相似文献   

13.
McMurdo dry valleys of Antarctica represent the largest of the ice-free areas on the Antarctic continent, containing glaciers, meltwater streams, and closed basin lakes. Previous geochemical studies of dry valley streams and lakes have addressed chemical weathering reactions of hyporheic substrate and geochemical evolution of dry valley surface waters. We examine cation transport and exchange reactions during a stream tracer experiment in a dry valley glacial meltwater stream. The injection solution was composed of dissolved Li+, Na+, K+, and Cl-. Chloride behaved conservatively in this stream, but Li+, Na+, and K+ were reactive to varying degrees. Mass balance analysis indicates that relative to Cl-, Li+ and K+ were taken up in downstream transport and Na+ was released. Simulations of conservative and reactive (first-order uptake or generation) solute transport were made with the OTIS (one-dimensional solute transport with inflow and storage) model. Among the four experimental reaches of Green Creek, solute transport simulations reveal that Li+ was removed from stream water in all four reaches, K+ was released in two reaches, taken up in one reach, and Na+ was released in all four reaches. Hyporheic sediments appear to be variable with uptake of Li+ in two reaches, uptake of K+ in one reach, release of K+ in two reaches, and uptake of Na+ in one reach. Mass balances of the conservative and reactive simulations show that from 1.05 to 2.19 moles of Li+ was adsorbed per reach, but less than 0.3 moles of K+ and less than 0.9 moles of Na+ were released per reach. This suggests that either (1) exchange of another ion which was not analyzed in this experiment or (2) that both ion exchange and sorption control inorganic solute transport. The elevated cation concentrations introduced during the experiment are typical of initial flows in each flow season, which flush accumulated dry salts from the streambed. We propose that the bed sediments (which compose the hyporheic zone) modulate the flushing of these salts during initial flows each season, due to ion exchange and sorption reactions.  相似文献   

14.
The impacts of common ions on the adsorption of heavy metal   总被引：1，自引：0，他引：1  
Researches on the impact of common ions onto sediments are of great importance for the study of the heavy metal adsorption mechanisms. Considering the surface sediments from the relatively clean reach in the Baotou section of the Yellow River as the adsorbent, this work presents the impacts of common ions (Na+, Mg2+, K+, Ca2+, Cl−, SO4 2−, and NH4 +) on heavy metals (Cu2+, Zn2+, Cd2+, and Pb2+) adsorption. The experimental results reveal that the adsorptive capacities of the heavy metals are controlled by different adsorption mechanisms in different ion concentration ranges. With the increase of the ionic strength, the adsorption of the heavy metals increases for the compression of the electric double layer, whereas decreases for the decreasing of the ionic activities of the heavy metals. The competitive adsorption and complexations between the heavy metals and common ions are also important factors controlling the heavy metal adsorption. According to the experimental results and the real concentration of common ions in the Baotou section of the Yellow River, the increase of the concentrations of Na+, Mg2+, K+, and Ca2+ would cause the increase of Zn2+ adsorption and reduce the Zn pollution. The NH4 + from the industrial discharge of the tributaries has a strong impact on the heavy metal adsorption.  相似文献   

15.
Caustic high level radioactive waste induces mineral weathering reactions that can influence the fate of radionuclides released in the vicinity of leaking storage tanks. The uptake and release of CsI and SrII were studied in batch reactors of 2:1 layer-type silicates—illite (Il), vermiculite (Vm) and montmorillonite (Mt)—under geochemical conditions characteristic of leaking tank waste at the Hanford Site in WA (0.05 m AlT, 2 m Na+, 1 m NO3−, pH ∼14, Cs and Sr present as co-contaminants). Time series (0 to 369 d) experiments were conducted at 298 K, with initial [Cs]0 and [Sr]0 concentrations from 10−5 to 10−3 mol kg−1. Clay mineral type affected the rates of (i) hydroxide promoted dissolution of Si, Al and Fe, (ii) precipitation of secondary solids and (iii) uptake of Cs and Sr. Initial Si release to solution followed the order Mt > Vm > Il. An abrupt decrease in soluble Si and/or Al after 33 d for Mt and Vm systems, and after 190 d for Il suspensions was concurrent with accumulation of secondary aluminosilicate precipitates. Strontium uptake exceeded that of Cs in both rate and extent, although sorbed Cs was generally more recalcitrant to subsequent desorption and dissolution. After 369 d reaction time, reacted Il, Vm and Mt solids retained up to 17, 47 and 14 mmol kg−1 (0.18, 0.24 and 0.02 μmol m−2) of Cs, and 0, 27 and 22 mmol kg−1 (0, 0.14 and 0.03 μmol m−2) Sr, respectively, which were not removed in subsequent Mg exchange or oxalic acid dissolution reactions. Solubility of Al and Si decreased with initial Cs and Sr concentration in Mt and Il, but not in Vm. High co-contaminant sorption to the Vm clay, therefore, appears to diminish the influence of those ions on mineral transformation rates.  相似文献   

16.
Hydrochemical studies were carried out in parts of Oban Massif and Mamfe Embayment, Southeastern Nigeria to examine the contributions of barite mining activities on water quality. Pond and stream water samples were collected from six abandoned barite mines and adjoining streams areas during dry and wet seasons. These samples were analysed for physicochemical parameters using standard techniques. The results showed that the quality of water samples in the vicinity of barite mine sites was characterized by low pH, low mineralization, high suspended solids and deep colour. Sodium (Na+) and calcium (Ca2+) are the dominant cations and bicarbonate (HCO3 ?) and sulphate (SO4 2?) the dominant anions. The low concentration of dissolved silica, relatively high concentrations of Na+, HCO3 ? and SO4 2? suggest a combined influence of silicate, carbonate and weathering of mine spoils. The total dissolved solids, total suspended solids, electrical conductivity and major ions (except Na+ and K+) are higher for water draining barite mines from Cretaceous sediments, while Na+, K+, Ba2+ are higher in basement rock areas. Correlation and factor analyses suggest that the main components of the water samples are related to anthropogenic, geogenic, mineralization and environmental controls, while Gibbs diagram plots indicate weathering as the main process controlling the chemistry of water. Computed values of hardness and some irrigational parameters showed that the pond and stream water samples are generally soft and can be used for irrigation. Generally, the water quality satisfied the WHO (2008) and NIS (2007) standards for domestic, agriculture and industrial. However, there is the need to assess the impact of the pollution on the ecosystem and human health while remediation measures are being considered.  相似文献   

17.
Diffusion experiments with HTO, 36Cl−, Br−, I−, 22Na+, 85Sr2+ and 134Cs+ at trace concentrations in a single sample of Opalinus Clay are modeled with PHREEQC’s multicomponent diffusion module. The model is used first in a classical approach to derive accessible porosities, geometrical factors (the ratio of pore tortuosity and constrictivity) and sorption behavior of the individual tracers assuming that the clay is homogeneous. The accessible porosity for neutral species and cations is obtained from HTO, the anion exclusion volume from 36Cl− and Br−, and the cation exchange capacity from 22Na+. The homogeneous model works well for tritium, the anions and 22Na+. However, the 85Sr2+ and 134Cs+ experiments show an early arrival of the tracer and a front-form that suggest a dual porosity structure. A model with 10% dead-end pores, containing 19% of the total exchange capacity, can satisfactorily calculate all the experimental data. The Cs+ diffusion model builds on a 3-site exchange model, constructed from batch sorption data. The excellent agreement of modeled and measured data contradicts earlier reports that the exchange capacity for Cs+ would be smaller in diffusion than in batch experiments.The geometrical factors for the anions are 1.5 times larger than for HTO, and for the cations 2-4 times smaller than for HTO. The different behavior is explained by a tripartite division of the porespace in free porewater, diffuse double layer (DDL) water, and interlayer water in montmorillonite. Differences between estimated and observed geometrical factors for cations are attributed to increased ion-pairing of the divalent cations in DDL water as a result of the low relative dielectric permittivity. Interlayer and/or surface diffusion contributes significantly to the diffusive flux of Cs+ but is negligible for the other solutes. The geometrical factors for anions are higher than estimated, because pore constrictions with overlapping double layers force the anions to take longer routes than HTO and the cations. Small differences among the anions can also be attributed to different ion-pairing in DDL water.  相似文献   

18.
《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   

19.
The results of experimental studies of ion exchange properties of Co-bearing ferromanganese crusts in the Magellan Seamounts (Pacific Ocean) are discussed. Maximum reactivity in reactions with the participation of manganese minerals (Fe-vernadite, vernadite) is typical of Na+, K+, and Ca2+ cations, whereas minimum activity is recorded for cations Pb2+ and Co2+. The exchange complex of ore minerals in crusts is composed of Na+, K+, Ca2+, Mg2+, and Mn2+ cations. The exchange capacity of manganese minerals increases from the alkali metal cations to rare and heavy metal cations. Peculiarities of the affiliation of Co2+, Mn2+, and Mg2+ cations in manganese minerals of crusts are discussed. In manganese minerals, Co occurs as Co2+ and Co3+ cations. Metal cations in manganese minerals occur in different chemical forms: sorbed (Na+, K+, Ca2+, Mn2+, Co2+, Cu2+, Zn2+, Cd2+, and Pb2+); sorbed and chemically bound (Mg2+, Ni2+, Y3+, La3+, and Mo6+); and only chemically bound (Co3+). It is shown that the age of crust, its preservation time in the air-dry state, and type of host substrate do not affect the ion exchange indicators of manganese minerals. It has been established that alkali metal cations are characterized by completely reversible equivalent sorption, whereas heavy metal cations are sorbed by a complex mechanism: equivalent ion exchange for all metal cations; superequivalent, partly reversible sorption for Ba2+, Pb2+, Co2+, and Cu2+ cations, relative to exchange cations of manganese minerals. The obtained results refine the role of ion exchange processes during the hydrogenic formation of Co-bearing ferromanganese crusts.  相似文献   

20.
Prokaryotes and cytoplasm of eukaryotes are dominated by K+, whereas the extracellular fluid of most species of multicellular organisms is dominated by Na+. It was substantiated that the K+/Na+ ratio in the salt constituent of the cells of modern organisms qualitatively reflects the proportions between these elements in the aqueous phase, in which the first forms of life and the protocell originated. The same conclusion is done by Armen Y. Mulkidjanian et al. (PNAS 13, 2012, E821-830). The chemical composition of primary aqueous phase of the Earth was reconstructed using thermodynamic numerical simulation of the equilibrium composition of the ??carbonaceous chondrite material-water??, ??primitive mantle material-water??, ??ultramafic rock-water??, ??mafic rocks-water?? systems that are open with respect to CO2 and CH4. It was shown that at 25°C, total pressure of 1 bar, and partial pressures of CO2 and CH4 10?5?C10?8 and 10?2?C10?8 bar, respectively, the aqueous phase of the systems with carbonaceous chondrite and primitive mantle has K+/Na+ > 1, which corresponds to the proportions of these elements in the intracellular solution. The aqueous phase is characterized by pH = 8?C9, Eh = ?450 ± 50 mV, the presence of ammonium nitrogen, and concentrations of K, Na, and Mg close to those in the inferred intracellular fluid. The interaction of water with ultramafic and mafic rocks provides K+/Na+ < 1 in aqueous solution, which corresponds to the chemical composition of the modern natural waters of the Earth??s crust. Simulation results show that the protocell could arise in the primary aqueous phase of the Earth during differentiation of chondritic material into the Earth??s core and mantle, after the formation of the nitrogen atmosphere containing CH4, CO2, NH3, H2, H2S, CO and other gases, but prior to the formation of the modern rocks of the Earth??s crust (first billion years of the planet??s lifetime).  相似文献   

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