Rate Of Cation Exchange Research Articles

Anion Exchange by Mixed-bed Ion Exchange at Ultralow Concentrations

The effects of the cation-to-anion resin ratio and the amount of resin on anion exchange performance was experimentally studied with mixed-bed columns. Three different amounts of resin and five different cation-to-anion resin ratios were selected, and 10-4 M NaCl solution was used. The experiments were performed in continuous packed bed ion exchange column with commercially available exchange resins. The performance was evaluated with the breakthrough curves obtained. The results showed that the shape of chloride breakthrough curves and the level of leakage depended on the amount of anion exchange resin based on the resin ratio. In addition, the selectivity coefficient for chloride-hydroxide exchange and the diffusion coefficient influenced the steepness and the pattern of breakthrough curves. It was expected that cation exchange rate could be higher than anion exchange rate depending on resin capacities. However, anion exchange rate was higher due to other parameters that influence ion exchange rate, i.e. the shape of breakthrough curve. They were selectivity coefficients, mass-transfer coefficients and diffusion coefficients of ions.

Development of modified flyash as a permeable reactive barrier medium for a former manufactured gas plant site, Northern Ireland

A sequential biological permeable reactive barrier (PRB) was determined to be the best option for remediating groundwater that has become contaminated with a wide range of organic contaminants (i.e., benzene, toluene, ethylbenzene, xylene and polyaromatic hydrocarbons), heavy metals (i.e., lead and arsenic), and cyanide at a former manufactured gas plant after 150 years of operation in Portadown, Northern Ireland. The objective of this study was to develop a modified flyash that could be used in the initial cell within a sequential biological PRB to filter complex contaminated groundwater containing ammonium. Flyash modified with lime (CaOH) and alum was subjected to a series of batch tests which investigated the modified cation exchange capacity (CEC) and rate of removal of anions and cations from the solution. These tests showed that a high flyash composition medium (80%) could remove 8.65 mol of ammonium contaminant for every kilogram of medium. The modified CEC procedure ruled out the possibility of cation exchange as the major removal mechanism. The medium could also adsorb anions as well as cations (i.e., Pb and Cr), but not with the same capacity. The initial mechanism for Pb and Cr removal is probably precipitation. This is followed by sorption, which is possibly the only mechanism for the removal of dichromate anions. Scanning electron microscopic analysis revealed very small (<1 μm) cubic highly crystalline precipitates on the flyash, although this new crystalline zeolite growth did not occur rapidly enough to enable productive zeolite formation. Surface area measurements showed that biofilm growth on the medium could be a major factor in the comparative reduction of surface area between real and synthetic contaminant groundwaters. The modified flyash was found to be a highly sorptive granular material that did not inhibit microbiological activity, however, leaching tests revealed that the medium would fail as a long-term barrier material.

Interaction of a Zwitterionic Surfactant with Synthetic Clays in Aqueous Suspensions: A Multinuclear Magnetic Resonance Study

1H and 13C NMR signal assignment of laurylamidopropylbetain has been obtained from 2D COSY, HETCOR, and HMBC pulse sequences. 13C and 14N NMR relaxation data show interaction of the polar head of the surfactant with low-charged clays dispersed in aqueous solution. The sodium cation exchange rate between the solid surface and the bulk is strongly affected by the charge of the clay layer, as seen from 23Na NMR data. Such an exchange is also observed with clay suspended in sodium dodecyl sulfate solutions.

石炭灰フライアッシュからのゼオライトのアルカリ水熱合成と生成物の陽イオン交換特性

The synthesis of zeolite from coal fly ash by alkali hydrothemal reaction with NaOH was investigated under various conditions and the physical properties of the products were measured in this study. The reaction rate of cation exchange and substitution ratio of calcium ion were examined with some solutions containing calcium ion. Also, some physical properties of calcium type zeolite were measured. Zeolite P which had large cation exchange capacity (about 500 meq / 100 g as CEC) was synthesized from coal fly ash under the particular synthesis condition; reaction temperature of 393 K, reaction time of 5 hrs, NaOH concentration of 1.5 mol / dm3 and solid-liquid ratio of 200 g / 800 cm3. The crystal type of synthesized zeolite changed from zeolite P to hydroxysodalite with an increase in concentration of NaOH. The reaction rate was obviously increased when the reaction temperature was over boiling point of water. It was confirmed that the cation exchange reaction of zeolite synthesized in this study could be almost reversible between calcium ion and sodium ion. Optimum condition for zeolite synthesis with high CEC and calcium substitution, and some factors affecting zeolite synthesis and cation exchange reaction were discussed.

The restriction of diffusion of cations at the external surface of cardiac myocytes varies between species

In cardiac muscle sarcolemmal structures such as T-tubules, caveolae and negatively charged protein-polysaccharides may affect the rate of cation exchange on the external surface of the cells. To test this hypothesis, we examined the rate of external cation exchange in adult rabbit and rat ventricular myocytes using a rapid solution switcher to change the bulk external solution within 4 ms. To assess the rate of diffusion of monovalent cations, we increased [K+]o from 4.4 to 6.6 or 8.8 mM and measured the time required to achieve a stable membrane depolarization. In rat myocytes, the mean time to 90% depolarization (t90) was significantly longer than that in rabbit myocytes (137 and 64 ms, respectively) and the difference in t90 was not associated with the cell size. To assess the time course of exchange of external Ca2+, we rapidly exposed the myocytes to 0 Ca2+-2 mM EGTA solution at specific time points before action potentials or voltage clamp steps, and measured the rate of alteration of the normalized peak [Ca2+]i transient (Flux-3) or Ca2+ current. Exposure to 0 Ca2+-2 mM EGTA solution caused a decline in the intracellular calcium transient. In rat myocytes, the rate of decline in the [Ca2+]i transient was much slower (t90 > 1500 ms, the time required for 90% decline) than for the rabbit (t90 = 295 ms). Also, the rate of decline in the Ca2+ current was prolonged in rat myocytes (t90 = 910 ms) compared with rabbit myocytes (t90 = 241 ms). These data indicate that there is a restricted space on the external surface of sarcolemma which limits diffusion of divalent cations more markedly than monovalent cations. The extent of this limitation of cation diffusion varies between species, and may have functional significance.

The mixed-bed ion exchange performance at ultralow concentrations 1. Variable feed concentration and incomplete mixing of resins

Experimental data were obtained to evaluate the performance of mixed-bed ion exchange for the cases of variable feed concentration and incomplete mixing of anion and cation resins observed in large scale industrial units. For variable feed concentration, step changes in feed concentration were arbitrarily introduced into a test column. For incomplete mixing, only anion resin was loaded in the upper 20% of the column and more cation resin in the lower portion. Feed concentrations of 5.0× 10−5−2.0×10-4 M NaCl were used for the experiments, with flow rates of 0.665-7.0 ml/sec. The effluent from the column was collected periodically and analyzed using on-line/off-line ion chromatography. The step changes in feed concentration affect the breakthrough times of sodium and chloride. Sodium breakthrough curve is more sensitive to the step changes than chloride breakthrough curve. With the same volumes of cation and anion resins, incomplete mixing of resins increases the cation exchange rate slightly and decreases the anion exchange rate slightly. As the cation resin volume increases, the effect of the incomplete mixing of resins decreases. The breakthrough curves of both ions, plotted as the ratio of effluent to the influent concentration versus run time in hour, give some detailed results about the effects of the conditions.

Natural Occurrence and Stability of Pyrochlore in Carbonatites, Related Hydrothermal Systems, and Weathering Environments

AbstractStoichiometric and non-stoichiometric (defect) pyrochlores crystallize during the magmatic and late magmatic-hydrothermal phases of carbonatite emplacement (T &gt; 450–550 °C, P &lt; 2 kb). Defect pyrochlores can also form at low temperatures in laterite horizons during weathering. After crystallization, pyrochlore is subject to alteration by hydrothermal fluids (T ∼ 550-200°C) and ground water. Alteration occurs primarily by ion exchange of low valence A-site cations together with O, F, and OH ions. The high valence cations Th and U are generally immobile; however, we have documented one example of hydrothermal alteration involving loss of U together with cation exchange at the B-site in samples from Mountain Pass, California. During laterite accumulation, the cation exchange rate of pyrochlore greatly exceeds the rate of matrix dissolution. The exceptional durability of pyrochlore in natural environments is related to the stability of the B-site framework cations. In carbonatites, defect pyrochlores may contain significant amounts of Si (up to 7.6 wt% SiO2) which is negatively correlated with Nb.

ATP dependence of NHE-1, the ubiquitous isoform of the Na+/H+ antiporter. Analysis of phosphorylation and subcellular localization.

ATP is not hydrolyzed during the transport cycle of the Na+/H+ exchanger (NHE), yet depletion of the nucleotide drastically reduces the rate of cation exchange. The mechanism underlying this inhibition was investigated in fibroblasts transfected with NHE-1, the growth factor-sensitive isoform of the antiport. NHE-1 was found to be phosphorylated in serum-starved, unstimulated cells. Acute ATP depletion induced a profound inhibition of transport without detectable changes in NHE-1 phosphorylation. Analysis of cells transfected with truncated mutants of NHE-1 indicated that the carboxyl-terminal cytosolic domain of the antiport is required for expression of its ATP dependence. To define whether inhibition of Na+/H+ exchange resulted from internalization of NHE-1, extracellularly exposed proteins were labeled with impermeant biotin derivatives. The proportion of NHE-1 exposed to the surface was comparable before and after ATP depletion. Immunofluorescence determinations revealed focal accumulations of NHE-1 on the membrane of untreated cells. NHE-1 redistributed following ATP depletion, showing a more homogeneous localization. F-actin, which co-localizes with the antiport in untreated cells, also redistributed when cells were ATP depleted. These findings suggest an interaction of NHE-1 with the cytoskeleton. Accordingly, disassembly of actin filaments with cytochalasin D induced redistribution of the antiport. However, Na+/H+ exchange activity was unaltered by cytochalasin D. We propose that ancillary proteins confer ATP sensitivity to the antiporter and may also mediate its association with the cytoskeleton. Depletion of the nucleotide would alter the interaction between NHE-1 and the putative regulator, inhibiting Na+/H+ exchange and inducing subcellular redistribution. However, disruption of the cytoskeleton at distal sites, such as induced by cytochalasins, is insufficient to inactivate the antiport.

Kinetics of ion exchange in polyphase systems including crystallizing substances

Kinetics of ion exchange has been investigated in triphase systems: (1) strong-base anion-exchanger AV-17 × 8 in the CO 3 2− form-CaCI 2 solution-CaCO 3 precipitate; and (2) sulfonate cation-exchanger KU-2 × 8 in the Ca 2+ form-Na 2CO 3 solution-CaCO 3 precipitate, and in quadriphase systems: (1) AV-17 × 8 in the CO 3 − form-CaSO 4 · 2H 2O precipitate-CaSO 4 saturated solution-CaCO 3 precipitate; and (2) AV-17 × 8 in the CO 3 2− form-KU-2 × 8 in the Ca 2+ form-Na 2CO 3 solution-CaCO 3 precipitate. It has been shown that in both tri- and quadri-phase systems, the rate of cation exchange is lower than that of anion exchange. The amount of the precipitate crystallizing on the surface of resin beads depends on the type of ion-exchange resin, its granulation and on the ratio of resin components in the case of quadriphase systems with a mixed bed. By varying this ratio and the granulation of the ion-exchangers it is possible to accomplish the precipitation mostly in the anion- or cation-exchanger. Under certain conditions the precipitation takes place mainly in the solution phase. The mathematical model of ion-exchange process accompanied by precipitation on the surface of the resin beads has been proposed. The rate of the ion-exchange process has been assumed to be controlled by diffusion within the porous layer of the precipitate fixed on the surface of the bead. As an example of practical application of the results obtained the method of simultaneous regeneration and separation of mixed bed resins exhausted in a water demineralization process has been proposed.

The influence of crown ethers on the rate of intramolecular cation exchange involving the 5,12-dihydrotetracene radical anion

The addition of dibenzo-18-crown-6 to the Na+–5,12-dihydrotetracene radical-anion ion pair has been found dramatically to reduce the rate of cation migration. The resulting e.s.r. spectra (which exhibit linewidth alternation) have been computer-simulated employing modified Bloch equations. The activation energy for the cation migration process has been found to be 19.3 kJ mol–1.

Rate of Cation Exchange on Clay Minerals as Determined by Specific‐Ion Electrode Techniques

AbstractA cationic electrode (used as a potassium specific‐ion electrode and a sodium specific‐ion electrode were used to measure rates of cation exchange on clay minerals. The Ba‐K exchange rates for kaolinite, illite, and montmorillonite were rapid with &gt;75% exchange being measured within 3 sec. Because this time interval represents response time of the specific‐ion electrode, the Ba‐K exchange on these clay minerals occurs at a faster rate than this and may be an instantaneous process. Ba‐K exchange on vermiculitic materials was characterized by both a rapid and a slow rate of exchange. A major part of the Ba‐K exchange in silt‐ and clay‐size vermiculite was found to be diffusion controlled.Ca‐K, Mg‐K, Ca‐Na, and Mg‐Na exchange rates were rapid for all vermiculites and other clay minerals used in the experiment. Only Poole vermiculite exhibited two rates of Ba‐Na exchange similar to those shown by all vermiculites during Ba‐K exchange. Ba‐Na exchange rates on all vermiculites except Poole were rapid.

The critical role of chloride in the correction of hypokalemic alkalosis in man

Studies of hypokalemic metabolic alkalosis in man have demonstrated that the provision of chloride is a prerequisite to restoration of normal acid-base and potassium equilibrium. In both experimentally-induced and diuretic-induced alkalosis the ingestion of a liberal quantity of dietary potassium had no effect on plasma bicarbonate concentration if chloride intake was simultaneously restricted. Furthermore, the administration of a dietary supplement of potassium in the form of bicarbonate or neutral phosphate also failed to correct the acid-base disturbance. Although potassium balance was slightly positive during loading with potassium bicarbonate or neutral phosphate, full repletion of body potassium stores could not be effected on the low chloride diet. By contrast, the administration of chloride as either the sodium or potassium salt led to a suppression of acid excretion with a prompt return of plasma bicarbonate concentration to normal; there was a simultaneous striking retention of potassium, and restoration of a normal serum potassium concentration. On the basis of these findings, and of earlier experimental observations in the dog, it has been proposed that so long as hypochloremia persists, a disproportion between the quantity of sodium reabsorbed and the amount of penetrating anion available for reabsorption (i.e., chloride) will maintain an accelerated rate of sodium-hydrogen and sodium-potassium exchange. This acceleration of the exchange process sustains both a high renal threshold for bicarbonate and prevents full repair of the potassium deficit. Only when chloride is made available can the accelerated rate of cation exchange be restored to normal. The possible implications of these findings in the treatment of hypokalemic alkalosis as it occurs in a variety of clinical settings are considered.

Studies on sodium-potassium-activated adenosinetriphosphatase. IV. Correlation with cation transport sensitive to cardiac glycosides

A systematic study was made of the occurrence in tissues with a cardiac glycoside-sensitive cation transport system of the enzyme sodium-potassium-activated adenosinetriphosphatase (NaK ATPase), which has been shown to function in the active transport of sodium and potassium in erythrocytes and to be specifically inhibited by cardiac glycosides. The enzyme was found to be present in significant quantities in all 21 tissues from 10 species studied. The activities ranged from 1.24 in human erythrocytes to 1825 in guinea pig brain, expressed in millimoles of adenosine triphosphate split/kg. wet weight of tissue/hr. at 37 °C. In 8 out of 12 tissues, where the cardiac glycoside-sensitive cation exchange rate could be calculated, a qualitative correlation was found between the cation exchange rate and the NaK ATPase activity. Inhibition curves were determined for the NaK ATPases of four different tissues from four species as a function of ouabain concentration. The slopes of the curves differed considerably, and the half-maximal inhibition concentrations varied over a 17-fold range. There was both a species effect and a tissue effect. The results were discussed from the point of view of the in vivo use of cardiac glycosides for the demonstration of NaK ATPase involvement in a physiological process. The distribution of NaK ATPase activity in centrifugal fractions of rat liver and brain homogenates was determined. In liver almost all activity was present in the “nuclear” fraction, while in brain the activity was spread over all three particulate fractions. No activity was found in the supernatant fractions. This pattern is consistent with predominant localization of the enzyme in the cell membranes of both tissues.

THE STRUCTURE OF THE COLLODION MEMBRANE AND ITS ELECTRICAL BEHAVIOR

1. The electronegative membranes described in the literature which show a high degree of ionic selectivity (permitting cations to pass and restricting the anions) have serious shortcomings: their absolute permeability is extremely low, much too small for convenient experimentation; their ionic selectivity in most cases is not as perfect as would be desirable, and is moreover adversely affected by prolonged contact with electrolyte solutions. 2. A method has been worked out to prepare membranes substantially free from these defects. Porous collodion membranes were cast on the outside of rotating tubes and then oxidized with 1 M NaOH. By allowing the oxidized porous membranes to dry in air on the tubes membranes of desirable properties are obtained. These membranes are smooth, have a well defined shape, and allow considerable handling without breaking. 3. This new type membrane when tested for ionic selectivity by the measurement of the "characteristic concentration potential," consistently gives potentials of 54 to 55 mv., the maximum thermodynamically possible value (at 25 degrees C.) being 55.1 mv. This high degree of ionic selectivity is not lost on prolonged contact with water, and is only very slowly affected by electrolyte solutions. 4. The absolute permeability of the new type membranes can be varied over a very wide range by changing the time of oxidation. Under optimum conditions membranes can be obtained with a resistance in 0.1 N KCl solution of only 0.5 ohms per 50 cm.(2) membrane area. The absolute rate of cation exchange through these membranes between solutions of different uni-univalent electrolytes is very high, in one case, e.g. 0.9 m.eq. cations per 4 hours, the anion leak being 0.02 m.eq. Thus, the absolute permeability of the new type membranes is two to four orders of magnitude greater than the permeability of the dried collodion membranes and the oxidized ("activated") dried collodion membranes used heretofore. Because of the characteristic properties of the new type membranes the term "megapermselective" (or "permselective") collodion membranes is proposed for them.