Abstract:

Organic matter adsorbed onto the surface of clay minerals is one of an important process in the natural environment.
However, the process and mechanism of the interaction between natural organic matter and clay minerals is highly debated due to its
complexity. To solve this problem, natural organic matter of L-lysine and chitosan are intercalated in montmorillonite. Chemical
analysis, infrared spectroscopy and X-ray diffraction have been employed in the characterization of the reaction products. Our data
indicated that the adsorption of the L-lysine and chitosan is both firstly dominated by cation exchange and secondly by adsorption of
electrically neutral forms. For L-lysine, three configurations seem to form. At low concentrations, L-lysine is inclined in the interlayer.
As the concentration of L-lysine increases, the molecules orientate perpendicular to the montmorillonitelayers, maybe in a zig-zag
arrangement. When the concentration is higher enough, the second row of L-lysine appears and peptides may formed in the interlayer
by L-lysine polymerisation. The net charge of amino acids, which depends on the pH value in both the bulk solution and in the
proximity of the clay layer or the interlayer space, is an important factor affecting the adsorption process. For chitosan, a layered
structure can form in the interlayer of montmorillonite. The pH value of the solution and the presence of the inorganic salt will affect the
adsorption process. Chitosan-montmor illonite complexes in aqueous solution at room temperature and atmospheric pressure is stable,
but under the same condition, L-lysine is easily released from the interlayer space of montmorillonite, which is related to the nature of
the organic matter itself and its form combined with montmorillonite.

Key words: montmorillonite；L-lysine；chitosan；adsorption；stability