Impact and repercussions of the Ostwald-de Izaguirre theory for adsorption from liquid mixtures: A 100-year perspective

The theory developed in 1922 by Wolfgang Ostwald and Ramón de Izaguirre for adsorption from solution is revisited one hundred years later, with a main focus on its impact and repercussions. A concise historical account is initiated with an examination of the circumstances under which that work was generated. After providing some biographic data about the authors' backgrounds at the time they developed it, a concise description of the so-called Ostwald-de Izaguirre theory is presented. This is followed by an assessment of its impact as a whole in the first decades after it was produced. Starting from about 1960, interest was focused on two separate outcomes from the theory: (i) the first classification of adsorption isotherms ever proposed, and (ii) an equation (Ostwald-de Izaguirre equation) that describes adsorption by solids of binary mixtures of miscible liquids and allows separating the contributions from both components of the solution. Although still in occasional use today, the isotherm classification made by Ostwald and de Izaguirre is of almost exclusively historical interest, having been displaced by Giles’ classification. Unlike this, the Ostwald-de Izaguirre equation is still used and, since it derives from a simple mass balance, there is general agreement that no assumptions were made that limit its use. Thus, it seems that there is nothing to prevent the applicability of this equation in the future.