Specific and non-specific adsorption of inorganic ions I. Evaluation of specific adsorbability by means of minimum concentration for specific adsorption

The Minimum Concentration for Specific Adsorption (MCSA) was defined as a reversal of the charge concentration of the ion at the infinite dilution of sol (adsorbent), or practically at such concentration of sol that equilibrium of the ion Is but negligibly affected by adsorption of the ion.

The MCSAs of 15 species of cations were measured with respect to SiO₂ at pH 4,6,5, and 10; the MCSAs of 10 species of anions were measured with respect to Fe(OH)₃ at pH 4, and 6.5; and the MCSAs of 10 species of anions were measured with respect to Al-coated-SiO₂ at pH 6.5. Relative specificities of the inorganic ions based on the MCSAs at pH 6.5 were as follows:

The MCSAs of cations with respect to SiO₂ and of anions to Fe(OH)₃ and Al-coated-SiO₂ at pH 6.5 had close relationships to ionic potentials and general solubility of the elements in water. Based on these results, the authors concluded that the MCSA could be used u an index of specificity (i.e. covalent bond-forming tendency) of an Jon at adsorption reactions.

The values corresponding to the apparent stability constants of surface complexes formed by adsorption reaction with SiO₂ and cations at pH 4 were calculated from the values of the MCSAs.