Interactions between chromate and surfactant modified montmorillonite at room temperature (25 degrees C) and different pHs (1-7) in aqueous solution in fixed bed columns have been studied. A series of column tests were performed to determine the breakthrough curves at different initial surfactant loadings (0.5-3 CEC) of the bed. The interlayer spacing increased with the surfactant loading from 14.2 to 40.5 angstrom. Experimental results of the column tests and the basal spacing of the column material showed that the adsorption of chromate onto the clay did not occur until the initial surfactant loading was beyond a critical concentration apparently enough to open the clay sheets for the entry of chromate species. The shapes of the breakthrough curves indicate that the chromate ions enter the interlamellar region only when the initial surfactant loadings are beyond 2 times the CEC of the clay. The amount of adsorbate increases proportionally with increasing bed depth. A simple two-parameter model originally introduced by Yoon and Nelson (Yoon, Y. H.; Nelson, J. H. Am. Ind. Hyg. Assoc. J. 1984, 45, 509) was used to calculate the breakthrough time. Chromate could be recovered completely by washing with ammonium hydroxide, and the column material was found to regain its capacity to adsorb repeatedly after simple acid wash.