Enhancement of adsorption efficiency of heavy metal Cu(II) and Zn(II) onto cationic surfactant modified bentonite

This study sought to enhance the metal adsorption capacity of bentonite by improving its surfaces. Surface modification by the cationic surfactant (Bencylhexadecyldimethyl ammonium chloride, BCDMACl) was successful in this respect, and was characterized by FTIR spectroscopy, XRF, BET, and swelling test. A major characteristic of BCDMACl is forming micelles that can intercalate into interlayers of clay and prevent swelling. The adsorption of Cu (II) and Zn (II) from aqueous solutions was studied in batch experiments, varying both contact time and concentrations of the metal ions. Retention of the metals in solution was detected by Atomic Absorption Spectroscopy (AAS). The adsorption data were fitted with Langmuir, Freundlich, and Dubinin-Radushkevich isotherm models, of which the Langmuir isotherm provided the best fit with experimental data (R2 range 0.962–0.993). The results also revealed that the modified bentonite had significantly improved adsorption capacities (qmax 50.76 and 35.21 mg/g for Cu(II) and Zn(II), respectively); about 2.5 and 2.0 fold improvements over natural bentonite. The pseudo-second-order rate equation provided the best fit to observed adsorption kinetics. This study demonstrated the modified bentonite as an effective adsorbent for the removal of heavy metals from aqueous solutions.