ENTHALPY OF INTERACTION OF ION-EXCHANGE HETEROGENEOUS MEMBRANES AND THEIR GRANULAR ANALOGUES WITH AMMONIUM NITRATE SOLUTION

Abstract

Ion-exchange membranes are widely used for extraction, separation and concentration of aqueous nitrogen-containing solutions. In the study the heterogeneous ion-exchange membranes of cationic type- MK-40, Ralex CM (H) -PP, MK-41 – and anionic type - MA-41, Ralex AM (H) -PP and also their granular analogues – cation exchanger  KУ-2·8 and anion exchanger AB-17·8 were used. Sorption of nitrate ions and ammonium ions was conducted from the ammonium nitrate solution with concentration of 0.012 mole / dm³. To determine sorption thermochemical characteristics of the studied ions the calorimetric method was used. It was found that for all the studied types of membranes and ion exchangers the processes were accompanied by heat evolution. From the calorimetric measurements the thermokinetic interaction curves of cation-exchange membranes and KУ-2×8 with the ammonium nitrate solution and anion-exchange membranes and AB-17×8 with the solution of the same salt were obtained. According to the curves the power of heat evolution and time of the process were determined. It was shown that the ion exchangers KУ-2·8 and AB-17·8 are characterized by a longer time to achieve the maximum of heat evolution and process time than for the similar membranes. This fact is explained by the different number and accessibility of the functional groups in the membranes and ion exchangers. From the thermo-kinetic curves the enthalpies of interaction were calculated. The process of the interaction between the granular ion exchangers and ions is characterized by higher values of the enthalpy than for the membranes which large steric effects are common for. Saline concentration, nature of exchangeable ions and type of functional groups of the ion exchanger and also its moisture content influence the enthalpy value. Experimental calorimetric data indicated that the energy costs connected with the effects of dehydration and conformational changes in the sorbent polymer chains do not overlap the exothermic sorption effect. The calorimetric method is informative to determine the nature and mechanism of sorption.