Cation Exchange Equilibria Research Articles

Internally-consistent geothermometry and H2O barometry in metamorphic rocks: The example garnet-chlorite-quartz

Temperature and H2O activity can be determined with high precision using metamorphic mineral assemblages that define both a dehydration equilibrium and a temperature-sensitive cation-exchange equilibrium. Such determinations are obtained by applying the Gibbs method and then integrating two resulting differential equations, as illustrated here for the assemblage garnet-chlorite-quartz. The first equation, a geothermometer that monitors temperature based upon Fe−Mg exchange between garnet and chlorite, was calibrated using rocks at Pecos Baldy, New Mexico: 0=0.05 P(bars)−19.02 T(K)+4607 ln K D+24,156 with errors of ±8°C based upon analytical precision. The second equation monitors differences in the activity of water between specimens (1) and (2): 0=(0.1 X Mg−chl, 1 − 2.05)(P 2 − P 1) +[−33.02+5.96 ln(X Fe−chl, 1/X alm, 1)][T 2−T 1 −2.67 RT 1ln[a(H2O)2/a(H2O)1] +5.96 T 1ln(X Fe−chl, 2 X alm, 1/X Fe−chl, 1 X alm, 2). For samples equilibrated at the same pressure and temperature, microprobe analytical errors of 1% limit precision to ±0.01 a(H2O). For samples equilibrated at the same pressure but variable temperature, uncertainty of ±8°C limits precision to ±0.06 a(H2O). Extreme presure sensitivity requires that the H2O-barometer be applied only to rocks where pressure gradients are absent or well-constrained. The geothermometer gives temperatures in agreement with two other garnet-chlorite geothermometers (Dickenson and Hewitt 1986; Ghent et al. 1987) and with garnet-biotite geothermometry (ferry and Spear 1978) over the temperature range 350–520°C. Application of the relative H2O barometer shows variations in the activity of water approaching 0.30 in several study areas. Either pelitic schists commonly equilibrate with a fluid that is not pure H2O, or some pelitic rocks undergo metamorphism in the absence of a free fluid phase.

Cation exchange equilibria between plagioclase and aqueous chloride solution at 600 to 700°C and 2 to 5 kbar

Cation exchange equilibria between plagioclase and aqueous chloride solution at 600 to 700°C and 2 to 5 kbar

DISTRIBUTION COEFFICIENTS AND ION EXCHANGE BEHAVIOUR OF SOME CHLORIDE COMPLEX FORMING ELEMENTS WITH BIO RAD AG50W-XB CATION EXCHANGE RESIN IN MIXED NITRIC-HYDROCHLORIC ACID SOLUTIONS

ABSTRACT Cation exchange equilibrium distribution coefficients are presented for the chloride complex forming elements Au(III), Tl(III), Hg(II), Bi(III), In, Cd, Zn, Pb(II), Fe(III) and Ga with a microporous (gel-type) resin of 8% DVB crosslinkage in hydrochloric-nitric acid mixtures ranging from 0.02M to 0.50M and from 0.20M to 2.0M concentrations, respectively. Separations which are possible by using mixtures and pure hydrochloric acid as eluting agents are demonstrated by three elution curves separating the mixtures Hg(II)-Cd-Zn; Au(III)-Bi(III)-Pb(II) and Tl (III)-In-Zn and the exchange behaviour of the elements is discussed.

Fluctuation model for compositional heterogeneity in skarn clinopyroxenes.

A model incorporating experimentally determined fluid-crystal cation exchange equilibrium constants is proposed to explain compositional variations in clinopyroxene from Japanese skarns. The proposed “Fluctuation Model” can account for the observed compositional heterogeneity in both individual and aggregate clinopyroxene grains on a thin section scale. The model assumes formation from a hydrothermal solution whose mean concentrations of magnesium, manganese and iron components remained essentially constant throughout crystal growth period at constant temperature and pressure. Compositional heterogeneity developed as a result of local spatial and temporal fluctuations about the mean solution component concentrations. The degree of fluctuation in the proportion of component i in the hydrothermal solution, as defined by the percent coefficient of variation, CVi, is linearly related to the mean mole percent, Mi, of the component in the hydrothermal solution by the equation CVi=0.25×(100-Mi). Various compositional patterns off naturally occurring skarn clinopyroxenes can be closely reproduced by the model.

COMPARATIVE DISTRIBUTION COEFFICIENTS FOR SOME ELEMENTS WITH A MACROPOROUS CATION EXCHANGE RESIN IN HNO3AND HCl

ABSTRACT Cation exchange equilibrium distribution coefficients are presented for the chloride complex forming elements Hg(II), Bi(III), In, Cd, Pb(II), Fe(III), Ga, Zn, Cu(II) and Te{IV) with a macroporous (macroreticular) cation exchange resin in nitric acid of concentrations ranging from 0.20 to 5.00 M.Known distribution coefficients (from the literature) for similar concentrations of hydrochloric acid are included for comparative purposes and the influence of chloride complex formation is discussed. Separations which are possible by using both HC1 and HNO3 as eluting agents are demonstrated by two elution curves separating the mixtures Hg(II)-Bi(III)-Zn-Pb(II); and Tl(III)-Bi(III)-Cu(II)-Fe(III).

THE INFLUENCE OF RESIN LOADING ON CATION EXCHANGE DISTRIBUTION COEFFICIENTS OF SOME ELEMENTS IN HYDROCHLORIC ACID

ABSTRACT Cation exchange equilibrium distribution coefficients are presented for Rb, Mg, Zn, Ba, Al, Yb, Th and Zr in several hydrochloric acid concentrations and using various amounts of the cations, ranging from 0.08 to 2.0 milliequivalents per gram dry AG50W-X8 strongly acidic cation exchange resin. A simple equation containing only distribution coefficients and concentration terms is developed which can be used for calculating trace amount distribution coefficients from those determined experimentally with larger amounts. The coefficients determined experimentally are used to test the validity and limits of the equation.

Whole equilibrium analysis of the inner- and outer-sphere chromium(iii)-phosphinate complex system

The stability constants of the inner- and outer-sphere chromium(III)-phosphinate complexes have been evaluated by two ion-exchange methods: one is the Donnan exclusion chromatography and the other is the cation-exchange equilibrium method: log K 1,0 = 2.7, log K 2,0 = 1.8 log K 3,0 = 1.3, log K 4,0 = 1.6 log K 5,0 = 0.71, and log K 6,0 = 0.079 for inner-sphere complexes; log K 0,1 = 0.90, and log K 0,2 = 0.079 for outer-sphere complexes; and log K 1,1 = 0.56 for the inner-outer mixed-sphere complex—all these being values at 50°C (20°C for K 1,1) and ionic strength of 0.2. Donnan exclusion chromatography has been proved as an effective method for such a system involving inert species. A total scheme has been clarified for this complex system under the conditions studied and the characteristic absorption spectrum of each chromium-phosphinate complex has also been established.

Cation Exchange Equilibria in Soils Expressed as Cation‐Ligand Complex Formation

AbstractA model for representing cation exchange reactions as part of the equilibrium reactions in a soil‐water system is proposed. The exchange reaction in this model is considered to be a composite of two half complexation reactions. These complexation reactions are assumed to occur between the exchanging cations and the negatively charged surfaces considered as hypothetical free ligands. The model was added as a subroutine to the GEOCHEM program which calculates ionic equilibrium in soil water systems. Two formation constants, K′Caf for the Ca‐ligand complex and K′Naf for the Na‐ligand complex were estimated by assuming K′2Naf/K′Caf = KVCa‐Na = 1 in the range 1 > ECa > 0.7. A value of log K′Caf = 2.5 was found to provide the best fit to the relationship between ES = (ENa/(CEC‐ENa)) vs. SAR given by the U.S. Salinity Laboratory Report (1954). The fitted value of K′Caf was used for calculating the K‐ligand formation constant; K′Kt and the Mg‐ligand formation constant, K′Mgr, using the appropriate experimental Vanselow selectivity coefficient. The calculated formation constants corresponding to the cations in a given soil water system were used to predict the distribution of the cations in solution and on the solid phase by means of the GEO‐CHEM program. Good agreement was found for the K‐Ca and Ca‐Mg exchange in soils when comparing experimental data to the ones predicted by the proposed model.

Conditions of high grade metamorphism in the Dalradian of Connemara, Ireland

In E Connemara, Ireland, Dalradian metasediments were initially metamorphosed to kyanite-staurolite grade at pressures above 7kbar. The subsequent emplacement of basic to intermediate magmas, accompanied by uplift and erosion, produce a steepening of the geothermal gradient and led to the formation of migmatitic garnet–cordierite–sillimanite-gneisses in the highest grade regions in the S. Cation exchange equilibria between coexisting mineral pairs suggest that partial melting took place under high temperatures (≃ 750°C) and moderate pressures (4.5–6 kbar). Fluid inclusion studies and andalusite occurrences from migmatite leucosomes suggest that crystallization of the melts occurred at lower pressures (<3.5 kbar) than melting, implying that uplift and erosion occurred while the rocks were hot.

Clay chemistry: Investigation of thermodynamics of ion exchange reactions by titration calorimetry

We have built a titration calorimeter that is suitable for measurements on colloidal suspensions as well as more conventional chemical reactions in solution. This calorimeter has been used for investigation of a number of ion exchange reactions involving kaolinite and montmorillonite clays. Results of these measurements have led to cation exchange capacities, to enthalpies of ion exchange reactions, and also to equilibrium constants for some of these same reactions. These calorimetrically determined cation exchange capacities and equilibrium constants agree well with corresponding quantities obtained by way of conventional methods based on chemical analyses. It has been demonstrated that titration calorimetry is a useful and convenient method for investigation of ion exchange in clays.

Column Chromatographic Separation of Hg(ll), La(lll), Ce(lll), and In(lll) from Other Metal Ions in NH4CI-CH3COOH Medium by Cation Exchange

Cation exchange equilibrium distribution coefficients (K) with the (Dowex 50W-X8) H/sup +/ form have been determined for 21 metal ions in media consisting of mixtures of 0.7 mol/dm/sup 3/ acetic acid and varying concentrations (0.16, 0.32, 0.48, 0.64, 0.96, and 1.28 mol/dm/sup 3/) of ammonium chloride. The distribution coefficients were determined by the batch technique for finding the conditions for the mentioned separations. The column chromatographic separations achieved were all quantitative. The results of the resolution of the synthetic binary and ternary mixtures along with the elution curves are presented. 3 figures, 4 tables.

Zeolite RHO. Part 2.—Cation exchange equilibria and kinetics

Exchange kinetics were measured in zeolite RHO for 2NH+4→ Ca2+, → Ca2+→ 2NH+4, 2NH+4→ Ba2 and Ba2+→ 2NH+4, all at 23°C; and for 2NH+4→ Ca2+ at 80°C. Exchange isotherms were determined at 80°C for the pairs NH+4⇌ Li+, Na+, K+, Rb+ and Cs+; Na+⇌ Cs+ and Ag+; and 2NH+4⇌ Ca2+, Sr2+ and Ba2+. In addition, the isotherms for NH+4⇌ Na+ and Cs+ were measured at 23°C.From the kinetic measurements diffusion coefficients were obtained and for all reversible isotherms thermodynamic equilibrium constants were evaluated. From the triangle rule equilibrium constants were then obtained for other combinations of the reversible exchange pairs. Kielland plots were determined and activity coefficients of the end members of the exchange (i.e., the homoionic forms) when admixed as the zeolitic solid solutions were evaluated as functions of the cationic composition. Trends in these curves for uni-univalent exchanges could be related to the differences between the ionic radii of the exchanging pairs. The thermodynamic affinity sequence for ions entering the zeolite was Cs+ > Rb+ > K+, Ag+ > NH+4 > Na+ > Li+ and Ba2+ > Sr2+ > Ca2+ for uni- and divalent ions, respectively.

Reclamation of Saline‐Sodic Soils by Leaching

AbstractSeven lysimeters containing sandy loam or clay loam soils were reclaimed by ponded or unsaturated leaching following a saline irrigation experiment of 2.5 years duration. Initial soil electrical conductivity was as high as ECe = 25 mmho/cm with associated exchangeable sodium percentages (ESP) up to 60%. Substantial quantities of solid gypsum and lime were present in the soil profile from precipitation reactions during the crop irrigation stage.Drainage volumes were expressed in pore volume units to scale out differences between water retention and leaching rates. Plots of scaled chloride concentrations (Cl/Cl initial) vs. pore volumes were similar for all lysimeters, with essentially all chloride removed by 1.5 pore volumes. Total salt removal was well described by a single curve (C/Cinft)(PV) = 0.8 for all treatments. Standard cation exchange equilibrium equations were used in a chromatographic displacement model to produce an algebraic equation to describe exchangeable Na reductions as a function of leaching pore volumes. This model, along with a model for calculating exchangeable Mg reductions, was in good agreement with measured changes for all treatments.No special amendments were required to maintain high permeability during leaching, even when distilled water was used, because of redissolution of previously precipitated Ca salts.

The Gapon and the Vanselow Selectivity Coefficients

AbstractA general thermodynamic relation between the Gapon and the Vanselow cation exchange equilibrium constants is derived and is shown to be violated by the expressions given traditionally in the soil chemistry literature for the Gapon and the Vanselow selectivity coefficients. This result suggests that the selectivity coefficient expressions are mutually in conflict. The traditional expression for the Gapon selectivity coefficient is shown to be in error, fundamentally because the Gapon convention—according to which cations react with an exchanger in equivalents—has no direct molecular interpretation. Therefore, the thermodynamic activity of an exchanger phase cannot be equated numerically with an equivalent fraction, even in some limiting case. The correct expression for the Gapon selectivity coefficient is derived and is discussed briefly for the case of Na‐Ca exchange. It is shown that the traditional expression and the correct one will not be very different numerically if the exchangeable sodium percentage is < 20.

On the Chemical Foundation of the Sodium Adsorption Ratio

AbstractThe theoretical chemical basis of the sodium adsorption ratio (SAR) was examined in order to clarify two important issues that arise in connection with the problem of estimating potential sodium hazard: (i) the relation between SAR and the theory of cation exchange, and (ii) the implications of the universal practice of replacing SAR by what may be termed the practical SAR, which employs total concentrations of Na, Ca, and Mg instead of their free cationic concentrations. In regard to (i), it was confirmed that SAR can be given a chemical basis in terms of the Gapon cation exchange equilibrium constant which is provided in this paper with a rigorous derivation for the first time. The Gapon constant is shown to differ from the Vanselow exchange constant only because of the (arbitrary) convention adopted as to what entity is termed the ligand in the cation exchange reaction. In regard to (ii), it was shown through a direct calculation of SAR and the practical SAR for 161 different soil solutions or water extracts, utilizing a comprehensive chemical equilibrium computer program, that an exact functional relationship between the two parameters does not exist. Only a statistical correlation between SAR and practical SAR could be established because of the random variation in the composition of metal‐complexing anions in the soil solutions or water extracts. These anions reduce the free cationic concentrations of Na, Ca, and Mg, but their amounts are not chemically related to the presence of the metals and, therefore, to the value of the practical SAR. It follows that the practical SAR has no exact chemical relation to the theory of cation exchange, although its use in strictly empirical studies of Na hazard may be justified, in a statistical sense, by its acknowledged practical value.

Acid precipitation effects on soil pH and base saturation of exchange sites

The typical values and probable ranges of acid-precipitation are evaluated in terms of their theoretical effects on pH and cation exchange equilibrium of soils characteristic of the humid temperature region. The extent of probable change in soil pH and the time required to cause such a change are calculated for a range of common soils. Hydrogen ion input by acid precipitation is compared to cation inputs from nutrient cycling and other sources. For example it can be calculated that 100 yr of acid precipitation (10000 cm at pH 4.0) could be expected to shift the percentage base saturation in the top 20 cm of a typical midwestern forest soil location exchange capacity of 20 meq 100 g−1 downward 20%, thus lowering the pH of the Al horizon by approximately 0.6 units, if there are no countering inputs of basic materials.

Cation-exchange equilibria on a Yolo loam

An experimental study was made of several cation-exchange reactions on a Yolo loam soil by means of a leaching procedure. Adsorption isotherms for the K-Na, K-Mg, K-Ca, and Mg-Ca ion pairs were obtained. An application of thermodynamic equations was used to find the equilibrium constants and free-energy changes for the reactions. Activity coefficients of the adsorbed ions were also calculated. A comparison of various selectivity coefficients was included.

Interacting Diffuse Layers in Mixed Mono‐Divalent Ionic Systems

AbstractA numerical solution of the electric double‐layer problem, for the case of overlapping diffuse layers in mixed monovalent‐divalent ion systems, is used to obtain a series of graphs for various cation compositions in the external solution. In these graphs, the electric potential is expressed as a function of the surface charge density, the concentration of the two cations in the equilibrium solution, and the distance between platelets in various ionic mixtures. The graphs cover most of the situations usually encountered in soil systems, and are not sensitive to the valency of the anions present. They are used to estimate the electrostatic effect on cation exchange equilibria, swelling pressures, and electrokinetic phenomena in mixed‐ion clay systems. Application of these estimates to theoretical analyses and comparisons between theoretical models and experimental data are illustrated. Some of the examples used for this illustration are based on work previously published by others.

Predictability of exchangeable sodium by gypsum requirement using cation exchange equilibria

Exchangeable Na of 106 surface soils correlated ( r = 0.507) with gypsum requirement (GR) and the correlation improved ( r = 0.657) after removing soils possessing high content of CaCO 3 and soluble bicarbonate. GR values correlated well ( r = 0.977) with exchangeable Na of five representative soils equilibrated with twenty solutions varying in salinity and SAR separately, as well as combined together. Exchangeable -Na status of field soils could be predicted better by gypsum requirement data using an empirical relation: Ex.fNa = 1.14 GR + 0.87, based on cation exchange equilibria.

Cation Exchange Characteristics of Some Metal Ions in Nitric Acid–Ammonium Acetate Medium

Abstract Cation exchange equilibrium distribution coefficients (A) with Amberlite IR-120 have been determined for 20 metal ions in media consisting of mixtures of 0.1 M HNO3 and varying concentrations, viz., 0.01, 0.05, 0.25, and 1.2 M, of ammonium acetate. The metal concentrations were so chosen that the ratio of total amount of cation to total resin capacity ≈ 0.4, sufficient to ensure exchange. The values of separation factors of various metal ion pairs have also been evaluated, and separation possibilities for ions in a number of binary and ternary mixtures have been proposed.