METAL ADSORPTION AND DESORPTION CHARACTERISTICS OF SURFACTANT MODIFIED CLAY COMPLEXES

Several modified clays have been designed and created for selective re moval and recovery of heavy metals such as Cd, Cu, Cr, etc. These surf actant-clay complexes were prepared using hectorite or montmorillonite as the base clay. A simple two-step approach has been developed to sy nthesize these modified-clay complexes through ion exchange and hydrop hobic anchoring of several surfactants such as long-chain alkyldiamine s, long-chain dialkylamines, and long-chain carboxylic adds onto the c lay matrices. The adsorption capacities and affinity constants of the modified clays can be found to approach those of commercial chelating resin (Chelex 100, Bio-Rad). Using cadmium as a model metal and ntmori llonite-cetylbenzyldimethylammonium-palmitic acid (M-CBDA-PA) as a mod el modified-clay complex, the maximum adsorption capacity of the modif ied clay is found to be 42 +/- 0.8 mg/g of clay and the affinity const ant is 3.0 +/- 0.1 mg/L. The metal adsorption has been shown to be mai nly through chemical complexation rather than ion exchange. The immobi lization of the metal ions is pH dependent, and thus, pH can act as a molecular switch to regenerate the modified-clay complexes.