Binary Exchange Research Articles

K - Ca - Mg binary cation exchange in saline soils from the north of Chile

The selectivities of the K–Ca and K–Mg cation exchange reactions were studied in batch experiments carried out with 7 Chilean saline sandy soils with low organic matter (OM) content, and rich in quartz and halite, by using the experimental Gaines and Thomas procedure and the semi-empirical Rothmund–Kornfeld approach. The soils present high reactivity to the exchange process in terms of CEC and a preference order from the surface for the cation of K > Ca > Mg. In addition, the existence of different types of exchange sites was determined; some were specific for determined cations and others presented free competition. The proposed exchange reaction for both equilibria was thermodynamically possible and the studied cations presented a decreasing mobility order K > Ca > Mg, which follows the increasing order of hydrated ionic radii. As for the Rothmund–Kornfeld semi-empirical approach, it can be employed on soils classified as Aridisol due to good fit with the experimental data. On the other hand, the Gaines and Thomas approach is only experimentally applicable since poses some restrictions concerning to salinity and carbonate contents in the studied soils.

Effect of the binary and ternary exchanges on crystallinity and textural properties of X zeolites

The ionic exchange of the NaX zeolite by Cu 2+ and/or Zn 2+ cations is progressively driven while following the development of some of its characteristic: crystallinity by XR diffraction, profile of isotherms, RI criterion, isosteric adsorption heat and microporous volume using both the Dubinin–Radushkevich (DR) equation and the t-plot through the Lippens–de Boer method which also makes it possible to determine the external surface area. Results show that the cationic exchange process, in the case of Cu 2+ introduced at higher degree, is accompanied by crystalline degradation for Cu( x)X, in contrast to Zn 2+-exchanged zeolite X. This degradation occurs without significant presence of mesopores, because the RI criterion values were found to be much lower than 2.2. A comparison between the binary and ternary exchanges shows that the curves of CuZn( x)X are clearly below those of Zn( x)X and Cu( x)X, whatever the examined parameter. On the other hand, the curves relating to CuZn( x)X tend towards those of Cu( x)X. This would again confirm the sensitivity of the crystalline structure of CuZn( x)X with respect to the introduction of Cu 2+ cations. An original result is the distortion of the zeolitic framework of X zeolites at middle exchange degree, when Cu 2+ competes with another divalent cation, such as Zn 2+, for the occupancy of sites distributed within zeolitic cavities. In other words, the ternary exchange accentuates the crystalline degradation of X zeolites. An unexpected result also is the noncorrelation between crystal damage and the external surface area.

Evaluation of exchange equilibria on strongly acidic ion exchangers with gel-type, macroporous and macronet structure

The effects of the structure of sulfonated polystyrenic resins of type gel, macroporous and macronet (hyper-crosslinked) on H+/Cu+, Zn2+, and Cd2+ binary ion exchange equilibria were investigated. The ion exchange isotherms were measured at 298K and 0.01 total equivalent concentration of the aqueous external solution using the atomic absorption spectrometry. Many equations were fitted to the experimental isotherms in order to investigate the energetic heterogeneity of the resin surface for the selected ions. The Langmuir isotherm seems to be a good approximation for all considered systems, within the experimental errors. It was shown that the fitted Langmuir isotherm could be used to determine the ion exchange equilibrium constants in the surface complexation model. The sorption constants and the ion exchange equilibrium constants of the surface complexation model give the same series of selectivity and affinity. For gel and macronet resins, the selectivity series is Cd2+>Zn2+>Cu2+, and for macroporous resin is Cu2+>Cd2+>Zn2+. The affinity of the macronet strong acid polystyrenic resin is higher than the affinity of the gel strong acid polystyrenic resin, for each investigated ion. The affinity of the macroporous strong acid resin compared with the gel and macronet is the highest for Cu2+, and the lowest for Cd2+. The ion exchange equilibrium constants for the selected counter-ions on the macronet resin present a notable variation, favoring a better separation, than on gel or macroporous resins.

Interpreting Unary, Binary, and Ternary Mixture Permeation Across a SAPO-34 Membrane with Loading-Dependent Maxwell−Stefan Diffusivities

Unary permeation experiments were performed with He, H2, CO2, N2, O2, CO, Ar, and CH4 across a SAPO-34 membrane at 295 K with upstream pressures ranging to 7.2 MPa, ensuring that high occupancies within the zeolite layer are reached. Careful analysis of the unary permeation experiments shows that the Maxwell−Stefan (M-S) diffusivity Đi is loading-dependent for all gases except He and H2. The model of Reed and Ehrlich (Surf. Sci. 1981, 102, 588−609) was used to describe the loading-dependence of Đi. The zero-loading diffusivity Đi(0) and the Reed−Ehrlich parameter φi are backed out from the permeation experiments, providing a complete description of Đi as a function of loading, qi. Permeation experiments for CO2/CH4, CO2/N2, N2/CH4, H2/CH4, H2/N2, H2/CO, and CO2/CH4/N2 mixtures were performed to determine to what extent loading-dependent M-S diffusivities influence permeation fluxes and selectivities. Good agreement between the M-S mixture model and experiments are obtained, provided the binary exchange co...

Influence of sodium adsorption ratio on sodium and calcium breakthrough curves and hydraulic conductivity in soil columns

The paper examines the effects of electrolyte concentration and sodium adsorption ratio (SAR) on the relative saturated hydraulic conductivity (RHC) and the ionic behaviour of calcium (Ca) and sodium (Na) ions in the Na–Ca exchange complex. Batch binary exchange and saturated column transport experiments were carried out to quantify these effects using an agricultural Balkuling soil and a mining residue. Generally, RHC has been found to decrease with time, with increasing SAR, and with decreasing electrolyte concentration. The more rapid decrease in RHC in the mining residue, particularly at the lowest concentration (1 mmol/L), was consistent at all SAR values. The decreases in RHC were likely to be caused by partial blocking of pores by dispersed clay particles, as evidenced by the appearance of suspended clay particles in the effluent during leaching. Significant differences in RHC were observed in the passage of fronts of decreasing electrolyte concentrations for CaCl2 and SAR 15 solutions through the soil columns. These differences were attributable to structural alterations (slaking) of the media and the nature of the particles released and mobilised within the porous structure at any given point in the column. Measurements at the critical threshold concentration and turbidity concentration at SAR 15 revealed structural breakdown of the pore matrix system as evidenced by decreased RHC. The increase in SAR to 15 is initially accompanied by erratic RHC, presumably due to the break up of soil aggregates under the increased swelling forces. The less coherent mining residue soil was substantially more vulnerable to blockage of pores than the Balkuling soil in which clay particles are likely to be more readily mobilised, and hence available to re-deposit and occlude the matrix pores.

Cation exchange reactions controlling desorption of 90Sr 2+ from coarse-grained contaminated sediments at the Hanford site, Washington

Nuclear waste that bore 90Sr 2+ 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. Sr 2+, 90Sr 2+, Mg 2+, and Ca 2+ was desorbed and total inorganic carbon concentration was monitored during the equilibration of this sediment with varying concentrations of Na +, Ca 2+. 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 90Sr 2+ to the water table.

A semi-analytical solution for linearized multicomponent cation exchange reactive transport in groundwater

Cation exchange in groundwater is one of the dominant surface reactions. Mass transfer of cation exchanging pollutants in groundwater is highly nonlinear due to the complex nonlinearities of exchange isotherms. This makes difficult to derive analytical solutions for transport equations. Available analytical solutions are valid only for binary cation exchange transport in 1-D and often disregard dispersion. Here we present a semi-analytical solution for linearized multication exchange reactive transport in steady 1-, 2- or 3-D groundwater flow. Nonlinear cation exchange mass–action–law equations are first linearized by means of a first-order Taylor expansion of log-concentrations around some selected reference concentrations and then substituted into transport equations. The resulting set of coupled partial differential equations (PDEs) are decoupled by means of a matrix similarity transformation which is applied also to boundary and initial concentrations. Uncoupled PDE’s are solved by standard analytical solutions. Concentrations of the original problem are obtained by back-transforming the solution of uncoupled PDEs. The semi-analytical solution compares well with nonlinear numerical solutions computed with a reactive transport code (CORE2D) for several 1-D test cases involving two and three cations having moderate retardation factors. Deviations of the semi-analytical solution from numerical solutions increase with increasing cation exchange capacity (CEC), but do not depend on Peclet number. The semi-analytical solution captures the fronts of ternary systems in an approximate manner and tends to oversmooth sharp fronts for large retardation factors. The semi-analytical solution performs better with reference concentrations equal to the arithmetic average of boundary and initial concentrations than it does with reference concentrations derived from the arithmetic average of log-concentrations of boundary and initial waters.

Modeling Permeation of CO2/CH4, CO2/N2, and N2/CH4 Mixtures Across SAPO-34 Membrane with the Maxwell−Stefan Equations

The objective of this paper is test the capability of the Maxwell−Stefan (M−S) diffusion formulation to predict binary mixture permeation fluxes across a SAPO-34 membrane using only data on pure-component adsorption isotherms and diffusivities. Experiments were carried out for permeation of CO2/CH4, CO2/N2, and N2/CH4 mixtures across a SAPO-34 membrane with upstream pressures ranging to 7.2 MPa, ensuring that high occupancies within the zeolite layer are reached. Good agreement between the M−S mixture model and experiments are obtained provided the binary exchange coefficients Đ12 in the M−S equations are assumed to have high enough values to ensure that intercage hops of the species occur independently of one other.

The Hill stability of a binary or planetary system during encounters with a third inclined body

The dynamical interaction of a binary or planetary system and a third body moving on a parabolic orbit inclined to the system is discussed in terms of Hill stability for the full three-body problem. The situation arises in binary star disruption and exchange, in extrasolar planetary system disruption, exchange and capture. It is found that increasing the inclination of the third body decreases the Hill regions of stability. This makes exchange or disruption of the component masses more likely as does increasing the eccentricity of the binary. The stability criteria are applied to determine possible disruption and capture distances for currently known extrasolar planetary systems.

The Redshift Distribution of Short Gamma-Ray Bursts from Dynamically Formed Neutron Star Binaries

Short-hard gamma-ray bursts (SHBs) may arise from gravitational wave (GW) driven mergers of double neutron star (DNS) systems. DNSs may be "primordial" or can form dynamically by binary exchange interactions in globular clusters during core-collapse. For primordial binaries, the time delay between formation and merger is expected to be short, tau~0.1 Gyr, implying that the redshift distribution of merger events should follow that of star-formation. We point out here that for dynamically formed DNSs, the time delay between star-formation and merger is dominated by the cluster core-collapse time, rather than by the GW inspiral time, yielding delays comparable to the Hubble time. We derive the redshift distribution of merger events of dynamically formed DNSs, and find it to differ significantly from that typically expected for primordial binaries. The observed redshift distribution of SHBs favors dynamical formation, although a primordial origin cannot be ruled out due to possible detection biases. Future red-shift observations of SHBs may allow to determine whether they are dominated by primordial or dynamically formed DNSs.

Adsorption behavior of strontium on binary mineral mixtures of Montmorillonite and Kaolinite

The adsorption behavior of kaolinite and montmorillonite minerals and their mixtures in respect of Sr ion were studied by means of a batch method using 90Sr as a radio tracer. The effect of several parameters such as temperature, pH, Sr concentration and supporting electrolyte were investigated. Experimentally measured distribution coefficients showed a good agreement to within 98.5–99.7% with theoretically calculated values. The values of adsorption capacity of adsorbents and mean adsorption energy of adsorption were calculated by fitting the adsorption data to Dubinin–Radushkevich isotherm. The adsorption capacity of clay mixtures decreased as kaolinite fractions increased. The mean adsorption energy values of 8.0–9.5 kJ mol −1 showed that adsorption was governed by ion exchange. The Freundlich parameters were used to characterize a site distribution function for binary exchange between Sr and Na.

Sorption of Np(V) on montmorillonite from solutions of MgCl2 and CaCl2

The Np(V) distribution coefficients between montmorillonite and solutions of MgCl2 and CaCl2 were determined experimentally. The Np sorption decreases with increasing concentration of the supporting electrolyte. The sorption is very fast within the first several hours after the start of the experiment and then decelerates, reaching the equilibrium in approximately two weeks. The constants of binary ion exchange NpO 2 + -Mg2+ and NpO 2 + -Ca2+ on montmorillonite determined by fitting the experimental results are $$\log K_{NpO_2^ + - Mg^{2 + } } = 0.083 \pm 0.03$$ and $$\log K_{NpO_2^ + - Ca^{2 + } } = 0.106 \pm 0.014$$ .

Sorption of Np(V) on kaolinite from solutions of MgCl2 and CaCl2

The Np(V) distribution coefficients between kaolinite and solutions of MgCl2 and CaCl2 were determined experimentally at various concentrations of the electrolytes and Np. The Np sorption decreases with increasing concentration of the supporting electrolyte. The sorption is completely reversible. The sorption equilibrium is attained in approximately one week after the start of the sorption-desorption experiments. The constants of NpO2+-Mg2+ and NpO2+-Ca2+ binary ion exchange on kaolinite were determined by fitting the experimental results with an ion-exchange equation for the restricted sorption capacity: \(\log K_{NpO_2^ + - Mg^{2 + } } = 1.26 \pm 0.08\) and \(\log K_{NpO_2^ + - Ca^{2 + } } = 0.96 \pm 0.10\). These constants describe well the experimental data at low Np concentrations (≤1×10−6 M). The ion-exchange capacity of kaolinite, calculated from the experimental data on Np sorption from solutions (3.03×10−4 g-equiv kg−1 MgCl2), somewhat differs from that in CaCl2 solutions (2.15×10−4 g-equiv kg−1).

Nietzsche's Pendulum: Oscillations of Humankind

Oscillations have been famously treated by anthropologists at the level of social structure. Rites of passage: dynamic equilibrium: binary exchange. Employing a Nietzschean trope of the Apollonian and Dionysian, this article treats oscillations more existentially. Between cultural belonging and truth, between symbolic form and experience, between poetry and biology—the article disinters certain motilities of being and becoming that exemplify universals of human capacity and can be claimed to be ubiquitous in human experience. Tensions are intrinsic to the human condition, the article argues, and knowledge of the human is also to be found between: between the orderly and formal on the one hand, and the gratuitous, random and free on the other. For instance, in an oscillation between cultural belonging and scientific truth, Ernest Gellner acceded to knowledge of a possibly universal, rational morality. Oscillating between the psychically intensive methodology and the extensive, George Devereux advocated knowledge of the potentialities of the human psyche as such. Oscillating between ideal‐typical, conceptual and symbolic schemata and the motile sensorium, between the biochemical conditioning of individual embodiment and the creative imagination, Edmund Leach and James Fernandez claimed knowledge of the connection between culture and society and bodily experience. Embracing oscillation one may approach an appropriately flexible and transitory knowledge of humankind, accepting the irony that it is ‘forms of movement’ that best give onto an appreciation of the human condition.

Kinetics of ion exchange in quasi-crystalline aluminosilicate zeolite precursors

The kinetics of binary ion exchange of Ca 2+ and Mg 2+ for Na + in quasi-crystalline and crystalline zeolite A has been investigated. Diffusion of either divalent cation into crystalline zeolite NaA is relatively fast, while the exchanges are slower in the quasi-crystalline precursor materials. The diffusion coefficient for Mg 2+ exchange ( D (Mg)) into crystalline zeolite A is an order of magnitude lower than that of Ca 2+ ( D (Ca)), due to the larger hydration sphere of the Mg 2+ ion. However, the ratio ( D (Ca): D (Mg)) was found to scale with the degree of crystallinity of the sample. Calcium and magnesium ions diffuse into the quasi-crystalline materials at comparable rates; this phenomenon is ascribed to the presence of larger pores in the quasi-crystalline structure, as compared to the crystalline material. Low impact mechanical treatment of quasi-crystalline zeolite precursors further decreases the difference between D (Ca) and D (Mg), while the crystallinity of the material is not noticeably decreased.

Evaluation of Soils for Use as Liner Materials: A Soil Chemistry Approach

Movement of NH(4)(+) below animal waste lagoons is generally a function of the whole-lagoon seepage rate, soil mineralogy, cations in the lagoon liquor, and selectivity for NH(4)(+) on the soil-exchange sites. Binary exchange reactions (Ca(2+)-K(+), Ca(2+)-NH(4)(+), and K(+)-NH(4)(+)) were conducted on two soils from the Great Plains and with combinations of these soils with bentonite or zeolite added. Binary exchanges were used to predict ternary exchanges Ca(2+)-K(+)-NH(4)(+) following the Rothmund-Kornfeld approach and Gaines-Thomas convention. Potassium and NH(4)(+) were preferred over Ca(2+), and K(+) was preferred over NH(4)(+) in all soils and soils with amendments. Generally, the addition of bentonite did not change cation selectivity over the native soils, whereas the addition of zeolite did. The Rothmund-Kornfeld approach worked well for predicting equivalent fractions of cations on the exchanger phase when only ternary-solution phase compositions were known. Actual swine- and cattle-lagoon solution compositions and the Rothmund-Kornfeld approach were used to project that native soils are predicted to retain 53 and 23%, respectively, of the downward-moving NH(4)(+) on their exchange sites. Additions of bentonite or zeolite to soils under swine lagoons may only slightly improve the equivalent fraction of NH(4)(+) on the exchange sites. Although additions of bentonite or zeolite may not help increase the NH(4)(+) selectivity of a liner material, increases in the overall cation exchange capacity (CEC) of a soil will ultimately decrease the amount of soil needed to adsorb downward-moving NH(4)(+).

Diffusion of Alkane Mixtures in Zeolites: Validating the Maxwell−Stefan Formulation Using MD Simulations

Molecular dynamics (MD) simulations have been carried out for pure components, binary, ternary, and quaternary mixtures containing methane, ethane, propane, and n-butane in FAU zeolite at 300 K for a range of molecular loadings Theta, approaching saturation limits. The n-dimensional matrix of Maxwell-Stefan (M-S) diffusivities [Delta], defined by (N) = -rho[Delta][Gamma](nabla Theta), was determined along with the self-diffusivities, D(i)(,self). Additionally, configurational-bias Monte Carlo (CBMC) simulations were carried out to obtain the pure component sorption isotherms and the saturation capacities Theta(i)(,sat). From the information on Delta(ij), D(i)(,self), and Theta(i)(,sat), the various M-S diffusivities were determined: (1) component D(i), reflecting the interactions of the species i with the zeolite, self-exchange D(ii), and (2) binary exchange D(ij). The obtained data underline the major advantage of the M-S formulation that at a given occupancy, theta = Sigma(N)(n)(i=l)Theta(j)/Theta(j)(,sat) within the zeolite, the D(i) has nearly the same value for species i whether this species is present on its own or in a mixture with other species. The same advantage holds, too, for the self-exchange D(ii); the value at a given occupancy, theta, is the same whether determined from pure component, binary, or ternary mixture data. For all binary and ternary mixtures studied, it was verified that the binary exchange coefficient D(ij) can be interpolated from the corresponding values of the self-exchange parameters D(ii) and D(jj) using a generalization of the interpolation formula developed earlier (Skoulidas et al., Langmuir, 2003, 19, 7977). We also demonstrate that if the occupancy dependence of the pure component parameters D(i) and D(ii) are modeled properly, this information is sufficient to provide very good estimates of the matrix [Delta] for mixtures with 2, 3, or 4 components over the entire range of loadings. Simulations of mixture diffusion of alkanes in MFI and LTA confirm that the above-mentioned advantages of the M-S formulation also hold for these zeolite topologies.

Modeling Multicomponent Ion Exchange: Application of the Single-Parameter Binary System Model

The single-parameter model for binary ion exchange equilibria is applied to the prediction of ternary and quaternary equilibria. This model is based on a statistical thermodynamic approach to exchanger-phase behavior, coupled with the Pitzer model for activity coefficients in aqueous solution and an explicit description of ion association phenomena. Exchange between alkali metal and alkaline earth cations on commercially available strong acid resins is investigated in the presence of a variety of nonexchanging anions. All systems can be predicted acceptably using parameters fitted to binary chloride-based systems. Model predictions from these parameters are highly accurate in many cases, while those systems that are not predicted as accurately from binary data are able to be described by recalculating one parameter using the ternary or quaternary data. This model fits all criteria required to be met by any description of ion exchange equilibria, and provides a simple yet highly effective approach to the description of equilibria in “real-world” ion exchange systems.

Multicomponent anion exchange with a resin having weakly and strongly basic groups

Multicomponent anion exchange with a resin having both weakly and strongly basic groups was investigated by means of modelling and column experiments. Our objective was to develop a model able to predict the evolution of the composition of a water treated by such a resin. The studied resin was Purolite S108, used for boron removal from water, on which ternary and quaternary amines were attached (additionally to boron complexing groups). Column dynamics were modelled with the computer code IMPACT, devoted to reactive transport in porous media. A reaction scheme was proposed to represent anion exchange on the two types of groups, with a quaternary anionic system including hydroxide, chloride, sulphate and nitrate at a given ionic concentration. This reaction scheme needed eight parameters: concentrations of weak and strong-base groups and the anion exchange selectivities. These parameters were measured through binary anion exchange, without or with pH step. The breakthrough curves of the binary experiments were in very good agreement with the experimental one. The model was then used to predict the results of a more complex experiment in which the column had been fed by a mixture of acids. The main features of the experimental behaviour were fairly well predicted, even if the agreement was not perfect. These discrepancies were attributed to the model assumptions, mainly to the expressions of anion exchange selectivities. These results enabled us to predict almost quantitatively the evolution of the water composition during its treatment. This point is an improvement in the prediction of the dynamics of an anion exchange with two types of groups. In the future, the model would have to be extended to take into account different expressions of the exchange selectivities, and nonequilibrium conditions.

Metallicity effects on open cluster dynamics

We take advantage of an N-body code that treats a range of metallicities to investigate the effect of metallicity on the internal dynamics of star clusters. Simulations of a set of large open clusters without primordial binaries are performed. We find that core collapse is postponed in low-metallicity star clusters, compared with Population I clusters, owing to the increased rate of mass loss through stellar evolution suffered at early times. However, earlier core collapse in high-metallicity clusters leads to an increase in the escape of stars from the cluster. We find that by remarkable cancellation of these two effects cluster dissolution times are little affected by changes in metallicity: high-metallicity clusters dissolve first but the difference is less than 10 per cent of the lifetime. We illustrate the behaviour of key structural properties of star clusters for models of different metallicity. We also look at the effect this has on the stellar populations of the clusters and the incidence of binary formation and exchange interactions. While the effect of metallicity on certain gross characteristics of a star cluster is found to be weak, we also find that in many respects metallicity is an important parameter in the evolution of a star cluster and should not be ignored.