The interaction between negative colloidal particles of NH4+-montmorillonite and particles of activated carbon was studied as a function of particle concentration, pH, and time of contact. The results show that carbon particles act as a support/bridge for clay particles, the type of resulting clay/carbon/clay associations depending on the pH and the clay/carbon ratio in the system. The relation between clay and carbon particles can be described by equations of the Langmuir type. For the same carbon particle concentration in the system, the relation varies from 6820 to 36, 100 and is dependent on pH. The interaction coefficients at pH 6.5 correspond to reaction of pseudo-first (k(1) = 4.14 x 10(-3) to 1.93 x 10(-3) s(-1)) and pseudo-second order (k(2) = 9.36 x 10(-14) to 2.47 x 10(-14) cm(3) s(-1)) for different clay/carbon ratios. By using the Dubinin-Radushkevich equation, the interaction energy ( +/- 22.42, +/-685.0, and +/- 14.63 J mol(-1)) was obtained for three different pH values (5, 6.7, and 7.6), demonstrating that the reaction is mainly physical. (C) 2007 Elsevier Inc. All rights reserved.