Modelling Zn(II) sorption onto clayey sediments using a multi-site ion-exchange model     

E. Tertre  C. Beaucaire  N. Coreau  A. Juery 《Applied Geochemistry》2009

In environmental studies, it is necessary to be able to predict the behaviour of contaminants in more or less complex physico-chemical contexts. The improvement of this prediction partly depends on establishing thermodynamic models that can describe the behaviour of these contaminants and, in particular, the sorption reactions on mineral surfaces. In this way, based on the mass action law, it is possible to use surface complexation models and ion exchange models. Therefore, the aim of this study is (i) to develop an ion-exchange model able to describe the sorption of transition metal onto pure clay minerals and (ii) to test the ability of this approach to predict the sorption of these elements onto natural materials containing clay minerals (i.e. soils/sediments) under various chemical conditions. This study is focused on the behaviour of Zn(II) in the presence of clayey sediments. Considering that clay minerals are cation exchangers containing multiple sorption sites, it is possible to interpret the sorption of Zn(II), as well as competitor cations, by ion-exchange equilibria with the clay minerals. This approach is applied with success to interpret the experimental data obtained previously in the Zn(II)–H⁺–Na⁺–montmorillonite system. The authors’ research team has already studied the behaviour of Na⁺, K⁺, Ca²⁺ and Mg²⁺ versus pH in terms of ion exchange onto pure montmorillonite, leading to the development of a thermodynamic database including the exchange site concentrations associated with montmorillonite and the selectivity coefficients of Na⁺, K⁺, Ca²⁺, Mg²⁺, and Zn²⁺ versus H⁺.  相似文献   

Effect of compacton on chemistry of solutions expelled from montmorillonite clay saturated in sea water     

GEORGE V. CHILINGARIAN  C. T. SAWABINI  HERMAN H. RIEKE 《Sedimentology》1973,20(3):391-398

The total mineralization of solutions squeezed out of montmorillonite clay saturated in sea water was determined at different overburden pressures. The subsequent fractions of expelled solutions were also analysed for various anions (Cl^?, SO^2-₄, HCO^?₃, F^?) and cations (Na⁺, K⁺, Mg²⁺, Ca²⁺, B³⁺). The results indicate that the concentrations of squeezed-out solutions during the initial stages of compaction (at pressures up to 35 kg/cm²) are slightly higher than that of interstitial solution present initially. The concentration of squeezed-out solution goes through a maximum, or at least remains constant, before starting to decrease with increasing overburden pressure.  相似文献   

Hydrogeochemical processes affecting groundwater in an irrigated land in Central Tunisia   总被引：7，自引：4，他引：3  

Intissar Farid  Rim Trabelsi  Kamel Zouari  Kamel Abid  Mohamed Ayachi 《Environmental Earth Sciences》2013,68(5):1215-1231

Detailed hydrogeochemical investigation has provided new information concerning the major factors and mechanisms controlling the groundwater chemistry of Chougafiya basin. The hydrogeochemical characteristics of groundwaters comprise three main types: Cl–SO₄–Ca, Cl–SO₄–Na and Cl–Na. Hydrochemical characteristics based on the bivariate diagrams of major (Cl^?, SO₄ ^2?, NO₃ ^?, HCO₃ ^?, Na⁺, Mg²⁺, K⁺ and Ca²⁺) and some trace (Br^? and Sr²⁺) ions, mineral saturation indices and hierarchical cluster analysis indicate different origins of groundwater mineralization. The water–rock interaction (dissolution of evaporitic minerals), followed by cation exchange reactions with clay minerals, constitute the main processes that control groundwater salinization. However, the chemical composition of brackish groundwater in the central and southern parts of the study area is influenced by a mixing process with Sabkhas salt groundwater. The mixing proportions inferred from chloride mass balance prove that the contribution of Sabkhas groundwater to Quaternary aquifer ranges between 2.7 and 9.1 %. These intrusion rates reflect the progress of the saltwater–freshwater interface, which is mainly controlled by the piezometric level variation and the distance to the Sabkhas.  相似文献   

Geochemical controls on lead concentrations in stream water and sediments     

John D. Hem 《Geochimica et cosmochimica acta》1976,40(6):599-609

The equilibrium distribution of lead in solution and adsorbed on cation exchange sites in sediment theoretically may be calculated from equations representing selectivities of substrate for lead over H⁺, Ca²⁺ and Na⁺, and the stabilities of lead solute species. Such calculations include consideration of total concentrations of major ions, cation exchange capacity (CEC) of substrate, and pH, at values expected in various natural systems. Measurements of CEC and selectivity coefficients were made for synthetic halloysite, a finely divided amorphous 1:1 clay prepared by precipitation from a mixture of solutions of aluminum and silica. Where suspended sediment having the same properties is present in concentrations of 10-1,000 mg/1 at pH 6–8, more than 90% of the lead present can be adsorbed on sediment surfaces. The cation exchange behavior of lead and other minor cationic species in natural systems could be predicted by this type of model if enough other supporting information were available. Information of the type needed describing natural stream sediments, however, is presently inadequate for accurate predictions.  相似文献   

Investigation of ammonia removal from polluted waters by Clinoptilolite zeolite     

A. R. Rahmani  A. H. Mahvi  A. R. Mesdaghinia  S. Nasseri 《International Journal of Environmental Science and Technology》2004,1(2):125-133

Ammonia nitrogen compounds in the wastewaters and effluents have harmful effects on water resources. Ion exchange with zeolites is a separation process for ammonia removal from effluents. The objective of this research was to study the efficiency of an ammonia removal and the factor affecting to this process. The Clinoptilolite was obtained from Semnan mines at the north part of Iran. The samples were grounded and sieved based on the U.S. standard mesh number 20, 30, 40 and conditioned by ammonia sulfate and sodium chloride solutions. The characteristics of samples for ammonia removal and the selectivity sequence for adsorbing interfering cations were then determined. Results shown that the average ion exchange capacity of zeolite in batch and continuous systems were 6.65–16 and 16.31–19.5 mg NH₄ ⁺ /g zeolite weight, respectively. In study on the zeolite for selective cations showed the ranking of K⁺, NH₄ ⁺, Na⁺, Ca²⁺ and Mg²⁺ respectively. Results indicated that high level of regeneration (95–98%) might be achieved with NaCl solution. Based on the results, Clinoptilolite may be effective applied in wastewater treatment, both from technical and economical aspects.  相似文献   

Chemical evolution of acid precipitation in the unsaturated zone of the Pennsylvanian siltstones and shale of central Ohio     

Yoram Eckstein  Valerie E. Lewis  James V. Bonta 《Hydrogeology Journal》2007,15(8):1489-1505

The North Appalachian Experimental Watershed in Coshocton, Ohio, USA has recorded average pH of precipitation of 4.7 over a 30-year period. The area lies within the Pennsylvanian siltstones and shale, dominated by aluminosilicates and <5% calcite. A study was conducted to determine the evolution of acid deposition through an unsaturated to saturated zone composed of siltstone and shale in an isolated hill, precluding lateral flow and seepage. The results from water–rock chemical reactions modeled using PHREEQM demonstrate the percolating precipitation water is neutralized to pH 7.5 within the top 1.5 m. The model suggests that, along with calcite, dissolution of albite, illite, and kaolinite are the dominant mechanisms of neutralization. The cation exchange capacity of the siltstone and shale, in the range 54.6–386 meq/100 g, appears to be a function of high organic carbon content of 2.0–3.2%. While cation exchange is responsible for some of the Na⁺ in solution, it is not the primary source of Ca²⁺, Mg²⁺, or K⁺ ions. Exchange onto clays is occurring, but is secondary to exchange on organic matter. Chemical composition of groundwater perched within a coal seam is controlled by oxidation and dissolution of pyrite, returning pH to approximately 4.0.  相似文献   

Effects of poor quality irrigation waters on the nutrient leaching and groundwater quality from sandy soil     

M. Jalali  H. Merrikhpour 《Environmental Geology》2008,53(6):1289-1298

Sodium (Na⁺) in poor quality irrigation water participate in ion-exchange processes results in the displacement of base cations into solution and a raised concentration in groundwater. Knowledge of the rate of decrease of nutrients from soils resulting from poor water quality application is essential for long-term planning of crop production while minimizing the impact on groundwater quality. In this study, we examined the effect of sodium adsorption ratio (SAR) of irrigation water on nutrients leaching and groundwater quality in columns of sandy soil. Three types of irrigation waters at three NaCl–CaCl₂ solutions with the following levels of SAR (5, 15, and 30) were synthesized in laboratory. With the application of solutions, exchange occurred between solution Na⁺ and exchangeable cations (Ca²⁺, Mg²⁺, and K⁺), resulting in the displacement of these cations and anions into solution. Increasing the level of SAR from 5 to 15 and 30 resulted in increase in the average exchangeable sodium percentage (ESP) of the soil from 10.4 to 20.3, and 32.5, respectively. Adverse effect of high Na⁺ concentration in the solutions on raising ESP was less pronounced in solution having low SAR. Leaching of Ca²⁺, Mg²⁺, K⁺, and P from soil with the application of solutions represents a significant loss of valuable nutrients. This sandy soil showed the high risk for nutrients transfer into groundwater in concentrations exceeding the groundwater quality standard. Irrigation with poor quality water, which is generally more sodic and saline than regional groundwater, increases the rate of sodification and salinization of shallow groundwater.  相似文献   

Nature of Co-bearing ferromanganese crusts of the Magellan Seamounts (Pacific Ocean): Communication 2. Ion exchange properties of ore minerals     

G. V. Novikov  S. V. Yashina  M. E. Mel’nikov  I. V. Vikent’ev  O. Yu. Bogdanova 《Lithology and Mineral Resources》2014,49(2):138-164

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   

The threshold value of epikarst runoff in forest karst mountain area     

Guanghui Jiang  Fang Guo  Jichun Wu  Huaju Li  Hailong Sun 《Environmental Geology》2008,55(1):87-93

Hydrochemical investigations were carried out in Damagh area, Hamadan, western Iran, to assess chemical composition of groundwater. Forty representative groundwater samples were collected from different wells to monitor the water chemistry of various ions. Chemical analysis of the groundwater showed that the mean concentration of the cations is in the order Na⁺ > Ca²⁺ > Mg²⁺ > K⁺, while that for anions was HCO₃⁻ > Cl⁻ > SO₄^{2 −} > NO₃⁻. All of the investigated groundwaters present two different chemical facies (Ca–HCO₃ and Na–HCO₃) which is in relation with their interaction with the geological formations of the basin, cation exchange between groundwater and clay minerals and anthropogenic activities. The principal component analysis (PCA) performed on groundwater identified three principal components controlling their variability in groundwater. Electrical conductivity, Mg²⁺, Na⁺, SO₄²⁻, and Cl⁻ content were associated in the same component (PC1) (salinity), determined principally by anthropogenic activities. The pH, CO₃^{2 −}, HCO₃⁻, and Ca²⁺ (PC2) content were related to the geogenic factor. Finally, the NO₃⁻, Cl⁻ and K⁺ (PC3) were controlled by anthropogenic activity as a consequence of inorganic fertilizers.  相似文献   

Influential factors on the levels of cation exchange capacity in sediment at Langat river     

Nur Aliaa Shafie  Ahmad Zaharin Aris  Nadzhratul Husna Ahmad Puad 《Arabian Journal of Geosciences》2013,6(8):3049-3058

An exploratory study was carried out at 22 sampling stations along the Langat River, Selangor in order to investigate on the vitality of cation exchange capacity (CEC) in sediment (0–5 cm). Parameters such as pH, Eh, salinity, and electrical conductivity (EC) were determined. The CEC in sediment has been calculated by the determination of Ca²⁺, Na⁺, Mg²⁺, and K⁺ using the flame atomic absorption spectrophotometer, while the organic matter content in sediment was ascertained using the loss on ignition method. The characteristic of the sediment shows that pH (3.09–7.46), salinity (0.02–10.71 ppt), EC (3.39–517 μS/cm) and Eh (?16.20–253.10 mV) were substantially high in variation. This study also revealed that exchangeable Ca²⁺ and Mg²⁺ were controlled by organic matter contents, while exchangeable Na⁺ and K⁺ were influenced by salinity. Salinity was observed to play a major part in controlling all the exchangeable cations, as it gives strong significant correlations with Na⁺, K⁺, Mg²⁺, CEC, and organic matter at p?<?0.01. The presence of seawater, clay mineralogy, and organic matter proves that it does play an important role in determining the CEC and soon relates to the pollution magnitude in the sediment.  相似文献   

Comparison of numerical simulation of solute transport with observed experimental data in a silt loam subsoil   总被引：1，自引：0，他引：1  

A. I. Paseka  M. Z. Iqbal  J. C. Walters 《Environmental Geology》2000,39(9):977-989

 Solute transport experiments were conducted on loamy soils of north-eastern Iowa, USA, and the results were compared with a numerical solution of a classical advection-dispersion transport model developed in this study. Flow experiments in the laboratory on undisturbed soil columns showed a flow rate of water much higher than was estimated from the soil properties and grain-size analysis data, suggesting preferential flow regime in the soil. In contrast, the relative concentration peaks of Cl^– and Br^– in the effluent were only approximately 70% of those predicted by the classical advection-dispersion equation (ADE). In addition, the experimental breakthrough curves (BTCs) showed greater tailings of these ions than the model solution. These observations suggest a loss of solute mass during transport from the dynamic flowing regions to a stagnant, immobile water phase in the soil matrix. Experiments in small disturbed soil columns showed that movement of Cl^– and Br^– is in good agreement with predictions of the classical ADE when the tracers are applied as a continuous source. However, in the case of a pulse source, the BTCs of Cl^– and Br^– matched the model only in the ascending part of the curves. Such variation indicates greater retardation of these ions than that of simulation, probably caused by the decrease in soil permeability due to cation exchange reactions in the soil involving monovalent and divalent cation pairs such as K⁺–Ca²⁺ and K⁺–Mg²⁺. In addition, retardation occurred as a result of the continuous saturation of soil columns which seemed to have caused an expansion of clay minerals, thus resulting in decreased soil permeability. In both the continuous and the pulse-source experiments, K⁺ was not detected in the effluent samples, which seemed to have been lost in exchange reactions and adsorption. Received: 20 November 1998 · Accepted: 19 July 1999  相似文献   

Reach-Scale Cation Exchange Controls on Major Ion Chemistry of an Antarctic Glacial Meltwater Stream     

Michael N. Gooseff  Diane M. Mcknight  Robert L. Runkel 《Aquatic Geochemistry》2004,10(3-4):221-238

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   

Correlative and comparative characterization of main ion concentrations in laterite groundwater in semi-arid northern Burkina Faso     

Julien Nikiema  Mario Schirmer  Walter Gläßer  Ronald Krieg 《Environmental Earth Sciences》2010,61(1):11-26

About 24 samples from hand-dug wells and boreholes were used to characterize concentrations of the main inorganic ions in a laterite environment under semi-arid climatic conditions in Tikaré, northern Burkina Faso. It was found that the most represented groundwater anion in groundwater was HCO₃ ⁻ with average levels of 49.1 mg/L in the dry season and 33.5 mg/L in the rainy season. The most represented cation was Ca²⁺ with mean concentrations of 13.7 and 9.5 mg/L, respectively. The main processes, which influence the concentrations of these ions, are evaporation (dry season), local enrichment of recharge water in some elements, ion exchange and fixation by clay minerals (in case of K⁺). The best correlations were found between Ca²⁺ and Mg²⁺ (r = 0.95), Cl⁻ and Na⁺ (r = 0.95), HCO₃ ⁻ and Mg²⁺ (r = 0.89), HCO₃ ⁻ and Ca²⁺ (r = 0.89), and between HCO₃ ⁻ and Na⁺ (r = 0.80). In general, the quality of the groundwater from the different wells sampled for this study was good enough to serve as drinking water. However, there were situations where the quality of water was polluted because of anthropogenic contaminants (mainly NO₃ ⁻, K⁺, Cl⁻) from septic tanks and manure pits located in the vicinity of some sampled wells. In addition, application of fertilizers also represents a potential anthropogenic contamination source with regard to SO₄ ²⁻, Ca²⁺, K⁺, Na⁺, and Mg²⁺. Considering the high concentrations of SO₄ ²⁻, Mg²⁺, Na⁺ and Ca²⁺ found in one borehole, the deeper, fractured aquifers were also likely to be enriched in these elements. In contrast, the shallow aquifers are likely to be contaminated with Cl⁻, NO₃ ⁻ and K⁺. Cl⁻ and K⁺ seem to be locally present in recharge water as shown by their relative higher mean concentrations in the rainy season samples.  相似文献   

Impact of anthropogenic activities on the chemistry and quality of groundwater: a case study from a terrain near Zarand City, Kerman Province, SE Iran     

S. M. Moosavirad  M. R. Janardhana  Houshang Khairy 《Environmental Earth Sciences》2013,69(7):2451-2467

Groundwater of an aquifer located in the vicinity of a large coal washery near Zarand City, Iran consists of two hydrochemically differing facies, which have been informally designated as groundwater (A) and groundwater (B). Groundwater (A) is native, brackish in composition and is characterized by Na⁺ > Mg²⁺ > Ca²⁺ > K⁺ and SO₄ ^2? > HCO₃ ^? > Cl^? > NO₃ ^?. Spearman’s rank correlation coefficient matrices, factor analysis data, and values of chloro-alkaline indices, C ratio and Na⁺/Cl^? molar ratio indicate that in the groundwater (A), the ionic load of Ca²⁺, Mg²⁺, Na⁺, K⁺, SO₄ ^2? and HCO₃ ^? is derived essentially from weathering of both carbonates and aluminosilicates and direct cation and reverse cation–anion exchange reactions. Groundwater (B) is the polluted variant of the groundwater (A), brackish to saline in composition, and unlike the groundwater (A), consists of HCO₃ ^? as the dominant anion. In comparison with the groundwater (A), the groundwater (B) contains higher concentrations of all ions, and its average ionic load (av. = 59.74 me/L) is 1.43 times higher than that of the groundwater (A) (av. = 41.54 me/L). Additional concentrations of Ca²⁺, Mg²⁺, K⁺, SO₄ ^2?, Cl^? and HCO₃ ^? in the groundwater (B) are provided mainly by downward infiltrating water from the coal washery tailings pond and reverse cation–anion exchange reaction between tailings pond water and exchanger of the aquifer matrix during non-conservative mixing process of groundwater (A) and tailings pond water. Certain additional concentrations of Na⁺, K⁺ and NO₃ ^? in the groundwater (B) are provided by other anthropogenic sources. Quality wise, both groundwaters are marginally suitable for cultivation of salt-tolerant crops only.  相似文献   

Sorption of Cesium on Clay Colloids: Kinetic and Thermodynamic Studies     

R. Deepthi Rani  P. Sasidhar 《Aquatic Geochemistry》2012,18(4):281-296

Sorption of radionuclides onto stable colloids can significantly enhance their transport in groundwater. Batch adsorption studies were performed to evaluate the influence of various experimental parameters like initial pH, contact time, temperature and concentration of Na⁺ and Ca²⁺ ions on the sorption of Cs on clay. The sorption process is dependent on pH of the solution with distribution coefficient (K _d) found to increase with increase in pH. The kinetic experiments were carried out at different temperatures, and the results have shown that the sorption process fits well into a pseudo-second-order mechanism with apparent activation energy of 45.7?kJ/mol. The rate constant was found to decrease with increase in temperature. The thermodynamic parameters such as ?G ⁰, ?H ⁰ and ?S ⁰ were calculated. The negative value of ?H ⁰ indicates that the reaction is exothermic. The negative values obtained for ?G ⁰ indicated that the sorption of cesium on clay was spontaneous at all studied concentrations. The distribution coefficient was found to decrease with increasing concentration of Na⁺ and Ca²⁺ ions. The cesium sorption data were fitted to Freundlich, Langmuir, Temkin and Dubinin–Radushkevich (D–R) isotherms. The values of Langmuir separation factor (R _L) indicate a favorable Cs adsorption. The values of mean free energy of sorption (E) at various temperatures ranged from 10.5 to 11.1?kJ/mol, which indicates that the sorption process follows chemisorption.  相似文献   

Compositional Variation of Hydrothermally Altered Volcanic Rocks in Hishikari Gold Epithermal System: A Useful Geochemical Indicator of Gold–Silver Epithermal Mineralization     

Naotatsu Shikazono  Hiroyuki Takahashi 《Resource Geology》2010,60(2):117-128

The hydrothermally altered andesite hosting the Hishikari gold-silver vein deposits in southern Kyushu, Japan, is analyzed with respect to the spatial variation in chemical composition. The (CaO + Na₂O) content is found to be inversely correlated with the K₂O content as it progresses away from the site of mineralization. It was found that analytical data plotted on a (CaO + Na₂O) − K₂O diagram cannot be explained only by addition of K⁺ from the hydrothermal solution to the original rock and release of Ca²⁺ and Na⁺ from the original rock (K- alteration). Addition of Ca²⁺ and Na⁺ from the hydrothermal solution to the rock and release of K⁺ from the rock but release of K⁺, Ca²⁺, and Na⁺ to the hydrothermal solution (advanced argillic alteration) is important for causing the wide variations in K₂O, CaO, and Na₂O contents on the (CaO + Na₂O) − K₂O diagram. These variations can be explained by superimposed potassic, advanced argillic and calcium alterations. The altered rocks in the Honko-Sanjin area, Yamada area, and Masaki area analyzed by this study are characterized by their intermediate K₂O content and variable CaO content, high K₂O content and low CaO content, and low K₂O content and low CaO content, respectively. The K₂O, Na₂O and CaO contents and oxygen isotopic composition of altered andesite, in conjunction with the solubility of gold as a thio complex, suggest that both gold deposition and the observed compositional variation of altered andesite are the result of mixing between acidic groundwater and neutral gold-bearing hydrothermal solution. The present results indicate that the compositional variation of hydrothermally altered rocks may represent a useful geochemical indicator of epithermal gold–silver mineralization.  相似文献   

Desorption kinetics of radiocesium from subsurface sediments at Hanford Site, USA     

Chongxuan Liu  John M. Zachara  James P. McKinley 《Geochimica et cosmochimica acta》2003,67(16):2893-2912

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   

离子色谱法同时测定铀矿浸出液中的阳离子   总被引：1，自引：0，他引：1  

李文娟  王志畅  刘金辉 《岩矿测试》2010,29(6):715-718

对铬铁矿中亚铁的测定方法进行了探讨。首先对已有方法进行了验证和筛选,然后对Li2SO4助熔剂的助溶作用及其反应机理进行了研究,从而推荐了H2SO4-H3PO4-V2O5-V(Ⅳ)-Li2SO4和H2SO4-H3PO4-Ce(SO4)2-Li2SO4两种改进型的溶剂体系用于铬铁矿试样中亚铁的测定,所得结果具有良好的重现性。  相似文献   

Structure and dynamics of water on Li-, Na-, K-, Cs-, H₃O-exchanged muscovite surfaces: A molecular dynamics study     

Hiroshi Sakuma  Katsuyuki Kawamura 《Geochimica et cosmochimica acta》2011,75(1):63-23407

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   

The coprecipitation of strontium,magnesium, sodium,potassium and chloride ions with gypsum. An experimental study     

Jacob Kushnir 《Geochimica et cosmochimica acta》1980,44(10):1471-1482

The coprecipitation of Sr²⁺, Mg²⁺, Na⁺, K⁺ and Cl^? into gypsum was studied as a function of temperature, brine concentration and growth rate. The concentrations of the studied cations in the gypsum increase with growth rate (kinetic effect), with a tendency to reach a limiting value at high growth rates. The partition coefficients of Sr tend to increase with brine concentration and decrease with temperature. The partition coefficients of the other cations also decrease with temperature but depend only very slightly on brine concentration. The concentrations of coprecipitated chloride are negligibly small.The coprecipitation behavior is explained in terms of the relation between the rate of desorption of the coprecipitating ions from the surface of the growing crystal, and the rate of growth. The studied cations may substitute for Ca²⁺ in its normal lattice sites and/or reside in interstitial positions among the structural water molecules. The relative amount of foreign cations occupying interstitial positions increases with increasing growth rate.The elucidation of the behavior of coprecipitated ions in gypsum given here forms a basis for the utilization of these ions as geochemical indicators for the environment of deposition of gypsum. These indicators may help in reconstructing important parameters such as temperature, brine concentration and growth rate.  相似文献