CHANGE IN THERMODYNAMIC CHARACTERISTICS OF HYDRATION OF CARBOXYL FIBER SORBENT IN EXCHANGE OF MAGNESIUM AND CALCIUM CATION

Abstract

The relationship between the characteristics of hydration and the selectivity of the fibrous carboxyl sorbent is established. Using the isopiestic method and thermal analysis, the hydration of the carboxyl fiber ion exchanger VION KN-1 in sodium, calcium and magnesium forms was studied. The quantity of absorbed water was determined, including the ratio of kinetically unequal water in the sorbent phase. The amount of water absorbed form of magnesium ion exchanger is greater than calcium, the molar proportion of water distribution varying in the degree of hydration of the magnesium and calcium forms fibers substantially equally. The changes in Gibbs energy of hydration and enthalpy of dehydration of ion-exchange fiber are calculated. The increase in Gibbs energy is due to the absorption of near- hydration water, and water farthest hydration is adsorbed at a constant value of the energy. Its highest values are determined for the magnesium form of the sorbent, and the least-for calcium, which corresponds to the ratio of the absorbed solvent of both forms in the first step of hydration. The exchange isotherms of calcium and magnesium ions on the sodium form of VION KN-1 fiber were obtained. The Gibbs energy of solvent interface transfer was calculated, which represents the difference between the Gibbs energies of ion exchange sorption and the direct exchange of cations, and describes the contribution of the change in sorbent hydration during the transition from one ionic form to another. It is found that the selectivity of extractable fiber ion exchanger to metal cations depending on the change in the sorbent during the hydration of ion exchange, which is energetically favorable process and promotes ion-exchange sorption. Carboxyl cation exchanger is more selective for magnesium ions than calcium ions, as confirmed by phase transfer energy high values solvent and less water released during the transition from the sodium form to the magnesium than during the transition to the calcium.