Changes in Amorphous and Crystalline Phases of Ion-exchange Membranes MA-41P and MK-40 in the Separation of Industrial Solutions by Electrodeionization and Electrodialysis Methods

The interest in studying the structure of ion-exchange membranes is degree of crystallinity, the interplanar distance and size of crystallites and other characteristics. This work aimed to study the change in structural characteristics of ion-exchange membranes MA-41P and MK-40 during electrodeionization and electrodialysis using X-ray diffraction (XRD) analysis and differential scanning calorimetry (DSC). For these processes, multicomponent solution model was used, which was similar in composition to industrial solutions used in galvanic production. It contained CuSO4, CoSO4, CdSO4, Fe(NO3)3 and Ni(NO3)2 with different initial concentration. As a result of the study, it was found that mechanical, chemical and thermal loads lead to the formation of defects and the gradual destruction of the membrane structure. The membrane becomes less selective, the ion transmission becomes less controllable, and undesirable reactions with the processed medium occur. The observed deviation of the diffraction angles at the crystalline peaks of water-saturated and working membrane samples indicates the sensitivity of macromolecules to mechanical and thermal loads arising under cyclic operation. This is due to a change in structural ordering, polymer matrix amorphization and intermolecular interactions within the membrane structure. A comparative analysis of the membrane structural characteristics after the separation processes has shown that the structure of the cation-exchange membrane MK-40 contains a larger percentage by 2–9 of the crystalline phase compared to the anion-exchange membrane MA-41P, which provides it with greater mechanical and chemical resistance during operation. In contrast, the anion-exchange membrane MA-41P is more amorphous and has a stronger absorption capacity.