The decrease in lead uptake by acid desorbent might be due to the increase of the concentrations of competing hydronium ions
Regarding the study about the influence of the pH over the material's adsorption capacity, it can be seen from Figure 2, that at pH 1, due to the high concentration of hydronium ions
, the adsorption of Cd(II) is drastically reduced.
A low pH indicates a high concentration of hydronium ions
, while a high pH indicates a low concentration.
When the positively charged droplets come into contact with the sample being tested, the hydronium ions
transfer their extra proton to molecules in the sample, turning them into ions.
Reducing the pH subsequently reduces the anion species available by increasing the competition amongst hydronium ions
and metal ions (24).
An essential part of this description is the theory of Esin and Markov (16) regarding specific occupation of adsorption sites in the inner Helmholtz plane (IHP) and outer Helmholtz plane (OHP) by hydronium ions
, hydroxide ions, electrolyte anions, and cations (two ion types for each Helmholtz plane have to be defined as preferentially adsorbed).