Addition of aliphatic amines to montmorillonite to improve its adsorption capacity for organic pollutants in aqueous solution
Adsorption is one of the prominent separation techniques used in the treatment of wastewaters containing soluble organics. Activated carbon has been employed almost exclusively in adsorbing the 129 "priority pollutants", as defined by the Environmental Protection Agency (EPA), from water and wastewater. Synthetic resins have recently begun to receive attention, but are derived from energy related sources, as is activated carbon. A few clays have been considered for use as adsorbents, but in nearly all cases the clays were used in their natural state. This research has explored the addition of the chloride salts of propylamine, dodecylamine, and dodecyldiamine to sodium montmorillonite (a smectite) in an attempt to improve its adsorptive capacity for removing organics from water and wastewater. X-ray diffraction analysis, differential thermal and thermogravimetric analyses, infrared spectroscopy, and scanning electron microscopy, were used to determine the interaction between montmorillonite and the alkylammonium salts. Replacement of exchangeable cations on the interlamellar surface of montmorillonite with alkylammonium ions has been shown by several researchers to permit ready intercalation of a wide variety of polar and nonpolar organic species. Adsorption isotherms conducted with acetaldehyde, acetone, benzene, butanol, chloroform, dimethylphthalate, hexanol, nitrobenzene, octanol, phenol, and toluene as the solutes showed some indication of intercalation of these eleven organic compounds. Intercalation of these compounds at low organic solution concentrations, 100 and 1,000 milligrams per liter, was found within the scope of the present study by x-ray diffraction and gas chromatography techniques not to be sufficient to make the alkylammonium-montmorillonites or the untreated montmorillonite totally competitive with current adsorbents used in the water and wastewater field. Adsorption of the eleven organic pollutants by the clays generally ranged from 10 to 50 percent of the amounts expected to be adsorbed on activated carbon at similar solute concentrations. Intercalation noted at high organic solution concentrations, up to 100 percent, was more significant and suggests the clays would be efficient in removing these organics at higher concentrations. X-ray diffraction results obtained make it possible to predict the orientation of the three alkylammonium ions and the eleven organic compounds in the interlamellar space of the montmorillonites.