Natural materials (e.g. wood, stone, sand, gravel and clay) are used in the nature found state without any prior processing. Bentonite is one of them. It is a remarkable material, with wide-ranging applications in the geochemical, building and pharmaceutical industries. This mineral is key component in the modeling process of ceramics, cements and sand formulation. The book presents the examination results of adsorption-desorption properties of materials based on bentonite. These properties are of a big importance because they belong to the mass transfer operations.