Investigation of the Causes of Appearance of Step-Shaped Form of Sorption Isotherm

The paper analyzes the causes of the appearance of steps with plateaus of different lengths in sorption isotherms, based on experimental and literature data. Examples of step-shaped isotherms are given to illustrate each type of causes. It is shown that the following factors can cause the deviation of sorption isotherms from linearity and the appearance of steps: sorbent polyfunctionality, the presence of sorption sites with significantly different specificity to sorbate; sorbate heterogeneity, the presence of inert sorbable sorbate species; chemical transformation of sorbents in the course of sorption with the formation of new phases, including processes involving solution components; sequential change of sorption mechanisms.