O. T. Gavlina

Effect of the temperature on the thermodynamic characteristics of the ion-exchange separation of substances on ionites

The basic results on the effect of temperature on the equilibrium and thermodynamic characteristics of ion-exchange systems and the use of this effect in developing reagentless methods for ion-exchange separation are considered.

The Differential Enthalpy of Ion Exchange on Selective Ionites

The problem of the experimental determination of the differential enthalpy of ion exchange is considered. The high errors in the enthalpies of ion exchange based on experimental corrected equilibrium coefficients substantially decrease the value of the parameters obtained this way. A method is suggested for finding the differential enthalpies of ion exchange on selective ionites on the basis of an analysis of only the composition of solutions in equilibrium systems at two temperatures. This allows the enthalpies to be determined with substantially lower errors than when traditional techniques are used.

Acid-base properties of phenol formaldehyde sorbents

It is shown that at a temperature of 295 K, phenol groups of phenol formaldehyde sorbents are characterized by the value pK ∼ 13.0–13.7. It is found that raising the temperature to 343 K reduces the pK value by one. It is concluded that the reason for the lower acidity of phenol formaldehyde sorbents relative to phenol in an aqueous solution is the smaller amount of firmly bound water.

The influence of temperature on the swelling of polyacrylic and polymethacrylic cationites

Temperature was shown to substantially influence the swelling of KB-2e3 polyacrylic and KB-4P2 polymethacrylic ionites cross-linked by triethylene glycol dimethacrylate (TEGDM) and divinylbenzene (DVB). Maximum swelling changes as the temperature increased were observed for the Ca form of the KB-4P2 ionite. Swelling and contraction of polymethacrylic cationite grains as the temperature decreased and increased occurred at equal fairly high rates, whereas the sorption of water by the polyacrylic cationite in the calcium form cross-linked by TEGDM occurred much more slowly than desorption.

Stability of phenol-formaldehyde ion-exchange sorbents in aqueous solutions

It is shown that ion-exchange sorbents based on phenol-formaldehyde resins can be used for a long time for isolating and separating rare alkali metals without any significant changes in the ion-exchange selectivity and capacity. When the phenol sorbents were used in alkaline solutions at elevated temperatures, carboxyl groups gradually accumulated in them as a result of the oxidation of methylol groups with oxygen dissolved in the solution. This led to a considerable increase in the ion-exchange capacity of the sorbents and a simultaneous decrease in the selectivity with respect to Cs+-Rb+ and Rb+-K+ ions (it is desirable to avoid the drying of phenol ionites in air by storing them in a swelled state in closed vessels).

The influence of temperature on the ion exchange properties of phenolformaldehyde sorbents

The influence of temperature on cation exchange on phenol groups of macroporous materials based on phenolformaldehyde resins (PFRs) was studied for Amberlit XAD 761 with irregularly shaped grains obtained by breaking up polycondensation resin blocks and FFS-1.4/0.7 with spherical granules. An increase in temperature caused some decrease in the sorption capacity of PFRs in the alkaline region, but almost did not influence the selectivity of alkali metal ion exchange. The sorption capacity and selectivity of PFRs did not change after multiple (dozens of cycles) transfer of phenol groups from the hydrogen to salt form and back. Ion exchangers of this type can effectively be used for separating mixtures of alkali metal ions containing cesium and rubidium.

Selectivity of ion exchangers in extracting cesium and rubidium from alkaline solutions

We compare the ion exchange selectivity of phenol-type sorbents based on phenol formaldehyde resins, products of condensation of diatomic phenols with formaldehyde, and crosslinked polymer based on C-phenyl[4]resorcinarene resin, for cesium and rubidium ions. It is shown that phenol formaldehyde sorbents are the ones most selective. The interaction of alkali metal cations with the anion of calix[4]arene is investigated via quantum-chemical modeling. It is shown that the selectivity toward cesium and rubidium ions in ion exchangers of the phenolic type is not due to specific interactions of ions with phenolic groups.

Dual-Temperature Reagentless Concentration of Solutions of Electrolytes Based on the Influence of Temperature on the Sorption of Water by Ionites

A new method of dual-temperature concentration and purification of pure and mixed solutions of calcium, magnesium, and sodium chlorides without solvent vaporization and the use of auxiliary reagents was studied. The method was based on the influence of temperature on the swelling of polymethacrylic and polyacrylic ionites. It was continuous solution passage through a column with a cationite with periodic temperature changes. A substantial increase in the concentration of solutions occurred at the “cold” stage of the process, and a decrease in concentration was observed at the “hot” stage.

The Temperature Dependence of the Exchange Enthalpy of Calcium and Sodium Ions on Polymethacrylic and Polyacrylic Cationites

The influence of temperature on the exchange of calcium and sodium ions from solutions of 2.3–2.8 g-equiv/l concentrations on KB-2e4 gel polyacrylic cationite, KB-4P2 and KB-4 gel polymethacrylic cationites, and Purolite C104 polyacrylic cationite was studied over the temperature range 273–400 K. It was shown that, simultaneously with a substantial increase in selectivity with respect to calcium ions, the differential enthalpy of the ion exchange reaction increased linearly on all polyacrylic and polymethacrylic cationites as the temperature grew.

A two-temperature concentration of alkali solutions on phenol-formaldehyde sorbents

The new phenomenon of a two-temperature non-reagent concentration of alkali solutions on sorbents based on the phenol-formaldehyde resin Amberlit XAD 761, PFR-1.4/0.7, and sulfonated phenol-formaldehyde ionite KU-1 was investigated. It was found that during an alkali solution’s passage through a column with a sorbent and a periodical change in temperature in the “cold” stage, the concentration of alkali in the filtrate appeared to decrease, while in the “hot” stage, the alkali concentration appeared to increase. It was shown that the increase in alkali concentration in a solution in contact with phenol-formaldehyde resin is determined by the ion-exchange properties of the phenol groups, and is associated with an increase in water dissociation upon a rise in temperature.