Adsorption of methylene blue on montmorillonite

Adsorption of Methylene Blue (MB) on Na-, Fe- and Al-montmorillonite suspensions at 298.15 K were studied. The effect of different exchangeable cation on the adsorption amount of MB was determined. The results show that methylene blue cations (MB+) replace Na+ more easily than they do Fe3+ and Al3+. The adsorption isotherms on the three montmorillonites were all of Langmuir type, except that the isotherm of MB on Na-montmorillonite presents nonmonotonic curve at low surface coverage. The specific surface areas in suspension were calculated by MB method, and Na+ is more effective to determine the specific surface area by MB method in suspension than Fe3+ and Al3+. The discrepancy of the specific surface area measured by MB and BET method was discussed.