The contact angle between a membrane surface and a waterdrop lying on its surface provides important information about the hydrophilicity/hydrophobicity of the membrane. This method is well-developed for solid non-swelling materials. However, ion-exchange membranes (IEMs) are gel-like solids that swell in liquids. When an IEM is exposed to air, its degree of swelling changes rapidly, making it difficult to measure the contact angle. In this paper, we examine the known experience of measuring contact angles and suggest a simple equipment that allows the membrane to remain swollen during measurements. An optimized protocol makes it possible to obtain reliable and reproducible results. Measuring parameters such as drop size, water dosing speed and others are optimized. Contact angle measurements are shown for a large number of commercial membranes. These data are supplemented with values from other surface characteristics from optical and profilometric measurements.

In recent years, due to the sharp increase in lithium demand, the interest in the problem of lithium recovery/extraction has increased dramatically: according to the Scopus database, about 3000 scientific publications on this issue appeared in 2021. The efforts of many specialists are directed towards the development of new, more economical and environmentally safe membrane technologies for lithium recovery to replace the existing reagent-based methods. This review integrates up-to-date data about the traditional and prospective methods for lithium recovery from natural solutions and leachates resulting from the disposal of spent batteries. The attention is focused on membrane methods. Known approaches are classified and analyzed, experimental and theoretical aspects of membrane-based ion separation are described; separation mechanisms and mathematical models are discussed. The review addresses pressure-driven and electromembrane processes, relatively well-developed at a laboratory level, which are used to extract lithium and other singly charged ions from mixed solutions containing large amounts of magnesium and calcium. The results of application of commercial and laboratory-made membranes are compared. Novel and emerging approaches suitable for effective separation of lithium ions from a mixture of singly charged cations, including hybrid electrobaromembrane methods, are considered. The bibliography includes 295 references