Ion Exchange at Edge and Interlayer in Montmorillonites Differing in Size

Science  05 Apr 1963:
Vol. 140, Issue 3562, pp. 75-76
DOI: 10.1126/science.140.3562.75


Titrations of hydrogen-saturated montmorillonite with sodium hydroxide indicate that two kinds of hydrogen are exchanged on the surface of the clay. At low pH there is more titratable hydrogen in a fine-size fraction of the clay than there is in a coarse fraction. This indicates neutralization of hydrogen adsorbed at the crystallite edge. The hydrogen adsorbed on the interlayer flake surface is neutralized at a higher pH, and there are more titratable hydrogen ions for the coarse fraction than for the fine. This suggests that surface-charge density is a function of crystallite size, a proposal already made on the basis of other properties of clay.