Abstract: Adsorption of a divalent quaternary ammonium named molecular deposition film flooding agent (MDFFA) on clay was studied. It is characterized by its surface non-activity. Two source clays were selected： montmorillonite (Su-M) and bentonite (B), and their cation exchange capacities (CEC) are 0.44 and 0.88 mmol•g^-1 clay, respectively. At low ionic strength, all cations were completely adsorbed on the clay. Besides, the absorbed amounts of MDFFA on Su-M reach 100% of the CEC, while the absorbed amounts of MDFFA on B only reach 77% of the CEC. From FT-IR spectra, we deduced that the MDFFA only binds to the electronegative adsorption sites and does not bind to the external Si－OH groups which act as neutral adsorption sites. XRD data show that the basal spacings of the two kinds of clay decreased slightly with added amount of MDFFA. Based on the theoretical size of molecules, we think that only horizontal monolayer of MDFFA exists in clay interlayer.

Key words: Adsorption, Molecular deposition filming flooding agent, Divalent quaternary ammonium complexes, Clay mineral