Charge determination at calcium salt/aqueous solution interface

It is shown that the fundamental potential determining ion system for Ca3(PO4)2 and CaCO3 particles is the Ca2+/anion pair rather than H+/OH–. In addition, the electrical capacity of the inner region of the electric double layer at the aqueous solution interface with both salts near their isoelectric points is ∼40 µF cm–2, with electrokinetic potentials equal to inner diffuse layer potentials.