Simultaneous adsorption of chlorophenol and heavy metal ions on organophilic bentonite

摘要

Organophilic bentonite obtained by ion exchange with benzyldimethyl octadecylammonium chloride has been used for multiple adsorption of 2-chlorophenol and the metals Pb~(2+) and Cd~(2+). This is of interest for the stabilization of wastes in which simultaneous organics/heavy metals contamination occurs. In such cases cement-based processes take advantage from the addition of quaternary ammonium salts exchanged bentonite. The results have shown that any of the contaminants is adsorbed according to a multilayer cooperative mechanism. Due to its organophilic nature, exchanged bentonite is able to adsorb 2-chlorophenol to a very high extent (about 0.7 g/g) when the organic is the only solute. On the other hand, each of the two metal ions is adsorbed to a much lesser extent when alone in solution (about 22 and 2.8 mg/g for Pb~(2+) and Cd~(2+), respectively). In the case of simultaneous presence of 2-chlorophenol and Pb~(2+) in solution, the adsorption isotherms of both solutes change to monolayer type and the adsorption capacity strongly decreases (about 0.3 g/g for 2-chlorophenol and 0.6 mg/g for Pb~(2+)). In the case of the 2-chlorophenol/Cd~(2+) systems, the adsorption capacity of about 0.3 g/g for 2-chlorophenol is retained, while Cd~(2+) is not adsorbed at all. In all the cases in which the bentonite is in contact with one of the metal ions, it has been checked that no exchange with the ammonium ions takes place. Finally, FT-IR analysis has shown that in all the cases investigated physical adsorption takes place and no new chemical bonds are formed.