Cation exchange capacities of safranin, toluidine and alizarin complexes with montmorillonite

To obtain information about the cation exchange capacity (CEC) of montmorillonite as affected by the sorption of charged organic molecules, montmorillonite samples were loaded with different amounts of positively charged molecules of safranin, toluidine blue, and negatively charged alizarin red S. Dye sorption by the clay was carried out by equilibrating samples with different concentrations of the dye. The adsorbed amounts were determined from initial and final dye concentrations using spectrophotometric methods. The CEC of the clay-organic complexes were determined by the BaCl{sub 2} base exchange capacity method. The CEC was found to decrease linearly with the increase in the amount of safranin and toluidine in the complex, giving rise to a 1:1 charge neutralization ratio. For alizarin the CEC increased linearly but was not in proportion to the amounts of alizarin in the complex. This noncumulative phenomenon was attributed to the hindering of free diffusion of exchanging cations by the adsorbed molecules.